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TNE WSS
INSTITUTE
INFORMATION AND
ADVISORY SERVICE
BULLETIN No. 10
APRIL, 1375
SMALL WATER SUPPLIES
Published by THE ROSS INSTITUTE
THE LOUDON SCHOOL OF HYGIENE ANO TROPICAL MEDICINE
Keppel Street (Gower Street), London, WC1E7HT
INFORMATION AND ADVISORY SERVICE
HE primary object of the Ross Institute is the prevention of
disease in the tropics. In the course of working towards this
end it has become apparent that the co-operation of industry
is essential if rapid progress is to be made. Fortunately, this
co-operation has never been lacking, for those responsible for
directing tropical industry were quick to appreciate the immense
value to them of healthy labour and have therefore been among
the strongest supporters of the Ross Institute since its inception.
T
For this reason the Ross Institute has made it an important
matter of policy to keep tropical industry informed of the progress
of medical knowledge, and of the practical methods by which the
greatest benefit may be obtained from its application. This series
of bulletins, which have been specially written for non-medical
people, is one of the means by which this information is made
available; other publications are issued from time to time and a
list of those now current will be found on page 62.
The Ross Institute invites all those whose work is connected
with the tropics to refer to it on any matter concerned with
health or welfare in tropical countries. The Director and his staff
will answer as promptly and as fully as possible all inquiries and
requests for advice.
2
SMALL WATER SUPPLIES
CONTENTS
Sources of Water
Rainwater
Surface Water ...
Ground-Water—Shallow, Deep, Artesian
The Basic Requirements of a Water Supply
Safe and Wholesome ...
Adequate Quantity
Readily Available
Selection of Source of Supply
Sources of Supply—Surface Water—Ground Water
Sanitary Survey
Sanitary Collection of Water
Rainwater
Surface Waters—
Streams
Ground-Water—
Infiltration Galleries
Springs
Wells—I land-dug, Sanitary precautions, Driven, Jetted,
Bore-hole, Drilled, Cleaning
Purification of Water under Rural Conditions
Sedimentation ...
Aeration
Filtration :—
Slow Sand Filters, Rapid Filters, Pressure Filters
Mechanical Filtration
Sterilisation—
Chlorination
Super-chlorination
Silver
Removal of Iron and Manganese
Hardness of Water
Removal of Salts
Purification of Water on a Domestic or Individual Scale
Disinfection—■
Boiling
...
...
...
.......................................
Chemical—Chlorine, Iodine
...
...
...
...
Domestic Filters—
Sand, Pressure, Ceramic candle, Kieselguhr candle ...
Silver—Katadyn and Sterasyl ...
...
...
...
Household Water Containers
...
...
...
...
Aerated Waters
...
...
...
...
...
...
Swimming Pools
...
...
...
...
...
...
3
PAGE
5
5
6
8
8
9
11
11
14
14
15
15
17
25
27
29
35
37
37
40
41
41
42
42
43
44
45
45
45
APPENDICES :
A : Chemical Standards for Drinking Water ...
...
47
B : Methods of Collecting
Chemical Examination
for
...
48
C : Bacteriological Standards for Drinking Water
recommended by the WHO Study Group ...
49
D : Collection of Water Samples for Bacteriological
Examination
...
...
...
...
...
51
E : Estimation of Quantity of Water Available
...
53
F : A Method of Jetting Small Diameter Wells
...
54
G : Relative Merits of Pumps for use in Small WaterSupply Systems'’
...
...
...
...
56
Water Samples
...
...
...
...
...
...
61
Publications of the Ross Institute...
...
...
...
62
Suppliers of Water Equipment
4
THE ROSS INSTITUTE INFORMATION
AND ADVISORY SERVICE
Bulletin No. 10
Reprinted April, 1975
{Originally issued June 1955, revised June 1957, re-written July 1961,
revised June 1964, revised June 1967, revised November 1971,
reprinted May 1974)
Small Water Supplies
Water is essential to life and it is also required for the maintenance
of personal and domestic cleanliness. Water, however, plays a pre
dominant part in the transmission of certain diseases of which man
himself is almost the only source. Thus, water may be beneficial or
malignant, depending on how it is treated. Those who provide others
with water for household purposes have a responsibility to see that the
water supplied is safe for human use. The following notes are intended
to help them in their task.
SOURCES OF WATER
Fresh water is derived from rain, hail, snow and dew. When rain
falls on the ground some of it evaporates; part of it—varying with the
amount and intensity of the precipitation—runs over the surface into
streams, rivers, lakes and ponds; and part of it soaks into the soil. Thus,
there arc three principal sources from which water for domestic purposes
may be obtained, namely rainwater, surface water, and ground-water.
Rainwater is really distilled water and is, therefore, pure but as it
falls it may pick up impurities from the atmosphere, e.g. soot, ammonia,
etc. near cities, salt near the sea and dust in dry regions. In most rural
areas this risk is remote and there rainwater is generally the safest of all
natural waters, provided it is properly collected and correctly stored.
In a few places, notably from the rock faces in Gibraltar, it is gathered
and supplied to communities, but in the great majority of cases it is
obtained by individual families from the roofs of their houses for their
own use. Rainwater is soft and particularly suitable for laundry purposes.
Surface Waters arc those of streams, rivers, ponds, lakes etc. and
their quality depends largely on their location. Water from hills and
valleys situated upland from human habitations and coming from
catchment areas where good sanitary control is maintained is usually
suitable for domestic use with little or no prior treatment. Rivers and
lakes in populated areas collect from villages and towns human and
animal wastes, and arc invariably heavily polluted. Self-purification
processes cannot be depended upon to render their waters bacteriologically safe, nor is clear water necessarily free from danger. Surface
waters are usually soft and, though they often contain organic matter
of vegetable origin, their inorganic content is usually low.
Ground-Water soaks into the ground and seeps downward till it
meets the first impermeable layer (sec Fig. No. 1). It then travels along
the incline of the layer to: (i) the point where the layer outcrops on the
surface and there the water appears as seepages, or springs: or (ii) it
reaches an area where water accumulates in the spaces of the soil, above
the first impermeable layer. This water is referred to as “shallow ground
water” and is the water that is tapped by the great majority of wells for
rural water supplies: or (iii) it infiltrates below an impermeable layer,
either where that layer appears on the surface, or through faults in that
layer. Such water accumulates above a deeper impermeable layer and
is then known as “deep ground-water.” In some places this deep ground
water is under such pressure that it is forced up a well and discharges
without pumping. Wells of this type arc known as “flowing” or
“artesian” wells.
Fig. No. 1 :—A diagram illustrating the subsurface layers and the
location of shallow and deep ground-water
Ground-water is seldom stationary' but moves slowly downward
along the impermeable layers at a rate determined by the permeability' of
the water-bearing layer (i.e. the “aquifer”) and the slope of the under
lying impermeable layer. The direction of the slope of these layers,
frequently, but not invariably, follows the contours of the surface of the
ground. As sanitary security requires that all sources of possible
contamination should be situated at a safe distance (100 ft. at least),
preferably down the underground stream, from shallow wells, the
direction of flow of the underground water is important. Special care
is needed in limestone areas as part of the formation is likely’ to be dis
solved by the water as it percolates through the layer causing open
“solution channels” to appear. Along such channels water, pure or
impure, may flow considerable distances.
6
As the result of the filtration which occurs as it seeps through the
soil ground-water is likely to be free of pathogenic bacteria and often it
may be used without further treatment. Frequently it can be found
near the houses and it is usually practical and economical to obtain.
The aquifer provides natural storage for the water at the point of intake,
but like a surface reservoir, it can be depleted if more water is taken from
it than enters it. In rural areas this is seldom a concern as the demands
arc generally small but it is advisable to check this point before in
stalling an expensive supply system. Gravels and sands are the best
water-bearing formations as they can hold large quantities of water
which they yield readily. Sandstone (especially if confined between two
impermeable layers) is another formation which may be tapped to
provide quantities of water. The chief disadvantages of ground-water
arc that it may have a high mineral content; it is sometimes hard; and it
usually requires pumping.
THE BASIC REQUIREMENTS OF A WATER SUPPLY
The objectives of any water supply, big or small, are to provide the
consumers with safe and wholesome water in adequate amounts and to
make that water readily available to users.
Safe and Wholesome Water has been defined as water that may be
consumed without risk from its chemical and bacterial content. Its
colour and odour should be unobjectionable and it should be free of
visible suspended matter.
Conditions vary so greatly in different parts of the world that it is
impossible to lay down rigid standards of chemical quality. Those
suggested by WHO arc to be found in Appendix A and the method
of collecting a sample of the water for chemical examination is detailed
in Appendix B. The bacteriological standards of drinking water
recommended by WHO arc quoted in Appendix C, ami the method of
collecting samples for bacteriological examination are outlined in
Appendix D.
Much valuable information concerning its sanitary quality may be
obtained by chemical examination of a water but it is impossible to say
that a water is free of sewage pollution by chemical analysis alone.
Where the presence of pollution is being investigated bacteriological
examination is essential. The results of the chemical and bacter
iological analysis should be co-related, but these examinations can refer
only to samples examined. A water which the tests have shown to be
safe may be polluted after the samples have been taken and the only
way of ensuring the early detection of intermittent pollution is through
frequent routine bacteriological examinations. In rural areas it is often
difficult enough to have one such examination done but to insist on
weekly repetitions would be quite unrealistic. Escherichia coli which
normally lives in the bowels of warm-blooded animals and which is
present in human faeces in enormous numbers is used as the bacterial
indicator of pollution. Unfortunately there is no ready method of
differentiating strains of E. coli of animal origin from those of human
origin.
In view of the foregoing it is of the utmost importance that the
supply system be correctly located and constructed so as to provide
natural protection against outside contamination. A careful inspection
of the pertinent area must, therefore, be carried out, and it should be
repeated at regular intervals to ensure that this area is maintained in the
necessary' sanitary state.
The demand per head will materially depend upon the method of
distribution to the consumers. Individual supplies to each family in
their respective homes should be the aim from a hygienic point of view,
but it is rarely that in a small African or Asian community’ this can be
achieved at the outset, and street fountains or standpipes will, as an
interim measure, be the source of water for a large proportion of the
population. Only experience within the particular country concerned will
8
show what actual demands arc likely to be, but something like this
pattern will emerge:
Water carried from a standpipe ... 25 litres per person per day
Water from a single tap in the home 50 litres per person per day
House with bath, wc, etc. ...
... 75-100 litres per person per day
Taking, as an example, a village community of 2,000 inhabitants, it
might be reasonable to assume an initial demand of 50 cubic metres per
day, rising to 75 cubic metres per day in five years’ time, and to 100 in
the future. Design would be based on the middle figure of 75, and
allowance made in the layout for this to be extended by one-third in
the future.
Readily Available : “From the purely public health view-point there
is no question but that the aim should be to supply safe and wholesome
water in adequate quantity to every family in its home”. Experience
on estates in Ceylon and elsewhere has shown that, when the workers
are provided with taps in their own houses they look after the taps and
the wastage of water is minimal. On the other hand, where the distri
bution of water to workers is by public stand-pipes, the taps arc gen
erally left running and many of them are repeatedly broken so that thev
cannot be turned off. Unfortunately the capital cost of a waterpoint in
each house is often too great and it is then necessary to compromise be
tween economic realities and public health principles.
Until they actually experience the benefits of safe water tropical
people rarely understand or appreciate its advantages and they will
continue to use their old polluted sources unless the new supply is
superior in some respects obvious to them, such as greater con
venience, or greater reliability. They may bathe themselves and wash
their clothes at the new waterpoints but the general standard of house
hold cleanliness will vary inversely with the distance the water has to
be carried. If the new waterpoints are not as handy or as dependable
as the old ones the people will continue to use unprotected shallow wells
near their homes or persist in going to the river for polluted water. Such
practices defeat the real object for which the new supply is being installed,
namely, to improve the public health. As many stand-pipes and house
hold connections as possible should, therefore, be supplied and the lay
out of the whole pipe system should be such as to facilitate the future
provision of a tap in each house. The following are suggested as min
imum standards
one stand-pipe should not serve much more than 40
people ; and in the case of wells to which the people must go for their
water there should be at least one well for every 250 people.
Even where water is in short supply people all too commonly
leave the public standpipe taps running and this, if unchecked, could
soon lead to an acute shortage of water. To deal with this problem
various types of press taps, c.g. the “Totem Tap”* (invented by T. N.
'Obtainable from the Colombo Commercial Company Ltd. Slave Island,
Colombo.
9
H. Marquis, a planter in Ceylon) have been tried. In many cases, how
ever, the users find a way of tying the press-cap back so that the water
continues to run without manual pressure on the tap. Many managers
deal with this by shutting off the water to the lines (or camps) for certain
suitable hours daily. One method of coping with the problem was
used on an estate in Ceylon. The manager constructed, at ground level,
one concrete tank to serve each 3 family quarters. The tank held an
adequate amount of water for one day for the people concerned and it
was filled from the pipe supply during the night. The workers obtained
their water from it by means of a pitcher-spout suction pump fixed to
the top of the tank (similar to the arrangement shown in Fig. No. 4).
Damages to the pump were not unreasonable. Another way of dealing
with water wastage was invented by the Engineers of Dunlop Malayan
Estates Ltd. They designed an ingenious cistern-pump which takes the
place of the usual stand pipe. This appliance, and the method of its
working are illustrated in Fig. No. 2.
Fig. No. 2 :—A cistem/standpipe. The water level in the cistern
is maintained by a ball valve on the inlet. The dipper is rotated by
the handle and on its passage through the water it scoops
up some. As the dipper continues on upwards it tips
this water into the open side of the axle pipe
and water flows along this pipe to the outlet.
SELECTION OF THE SOURCE OF SUPPLY
The choice of source of supply for development depends on a
number of factors: the quantity and quality of the water available;
the possibilities of sanitary control of the catchment area; whether the
water can be supplied to the consumers by gravity or has to be pumped;
and the distance from the source to the houses. In order to obtain full
information on these points it is necessary to carry out a very careful
preliminary' survey.
10
Sources of Supply
The first step in starting any water scheme is to ascertain what
sources of supply arc available. Frequently a good source is not difficult
to find but it is usually advisable to check all alternatives as some, though
less evident, may be more economical and safer to develop. Some
times suitable sources are not obvious and a search should then be made
in the valleys, along the foot of the hills, where the vegetation is greener,
and such places. In this reconnaissance the inhabitants are generally
very willing to assist with their local knowledge.
If the quest fails to reveal a satisfactory source an investigation of
the ground-water becomes necessarj’, and for this a knowledge of the
local geological formations is most helpful but usually there are no
records available. A study of any existing well will provide some in
formation about the layers it penetrates, and the location, quantity and
quality of the water. Unless a good deal is already known about the
aquifer it is expedient to sink test holes at various likely spots. (See
Fig. No. 3.) These holes may be made with a pipe, about 2 inches in
diameter, tipped with a point, and driven into the ground by a hammer,
or a pipe sunk by an earth auger or by boring. A reasonably practical
man can generally cope with this, provided the waler is not more than
30 feet or so from the surface. If it is necessary to probe the potent
ialities of the deep ground-water, however, it is wise to obtain the
services of an engineer possessing the experience and the equipment
for this type of work. Deep well exploration and construction are ex
pensive and are not jobs for amateurs.
The next step is to ascertain the quantity of water available, by the
methods described in Appendix E. The rainfall figures may be obtained
and the history of springs and existing wells may often be secured from
the local residents. An estimate of the capacity of the aquifer may be made
by pumping a well and noting the rate at which the well refills but the
approximate yield in the dry season must be determined as that is often a
decisive factor.
The Sanitary Survey
The sanitary conditions prevailing in the immediate environs and
catchment areas of possible sources should be thoroughly investigated.
This is most important because the methods of purification of water,
under rural conditions, are limited, and the process is too often neglected.
Animal contamination of the water is very undesirable, and in some
places may be dangerous, but the greatest hazard lies in pollution from
human sources. It may be possible to find a spring, or stream, coming
from a safe catchment area situated uphill from human habitation, or
it may be practicable to render a source safe by moving potential origins
of contamination or to protect the source by suitable intercepting
drainage etc. Though the water from a stream may be liable to pollution
it is often feasible to obtain wholesome water through wells and in
filtration channels sunk in sand and gravel layers near the stream.
11
A =■ Tripod
B = Sheave wheel
C = Rope
D = To motor winch
E «=■ Drive hammer
F *=* Jar length
G ™ Drive head
H = Rod coupling
I =■ Drill rod
L •• Casing drive head
M — Rod drive head
N “ Casing drive shoe
Lifting bail
O
P ■=■ Water swivel
Q “ Pump
R = Suction hose
S «= Tank
by drive
T ■= Tee, replaced
head when driving casing
K «= Chopping bit (This may be replaced with a sampler
if desired. The water swi'
is then replaced by
a rod drive head.)
(Reproduced from WHO Monograph Series No. 42)
Fig. No. 3 :—Shows simple equipment for making exploratory
holes. Casing is driven into water-bearing formation, and cuttings
are washed out. Undisturbed samples can be taken at necessary
intervals. Well screens may be set in holes for test pumping
when desirable.
12
Wherever possible the water should be examined chemically and
bactcriologically and residts considered in the light of the sanitary
survey.
In the final selection, the waler which needs no purification to bring
it up to the recommended physical, chemical and bacteriological stand
ards is to be chosen before water that requires some treatment, and
water that can be supplied by gravity is commonly to be favoured over
water that entails pumping. Of these two qualities the water that
requires no treatment but needs pumping is generally preferable to
the water which needs treatment but no pumping. The first choice,
namely water that demands neither purification nor pumping, is ordin
arily restricted to springs and streams in protected drainage areas
situated uphill from human habitations.
Fig. No. 4 :—A domestic sand filter and water cistern
13
THE SANITARY COLLECTION OF WATER
The methods of collecting water so as to protect it against pollution
vary with the source and the circumstances. The general principles of
the methods needed are described below.
Rainwater: The collection of rainwater requires that roofs and
roof gutterings arc as clean as practicable. The roofs should be of tiles,
slates or sheeting (G.I., aluminium or asbestos) and not of thatch or lead.
The guttering should be well graded and free of sagging (this also avoids
the occurrence of pools which would form suitable breeding places for
mosquitoes). Dust, dead leaves, bird-droppings etc. are liable to
accumulate on the roof and in the gutters during dry periods and it is
advisable to run to waste the first water of each shower. This may be
done by means of a manually, or automatically, operated separator
installed in the down-pipe from the roof. Both types of separator are
available. It is also advisable to extract from the water any suspended
matter which it may contain. A metal strainer or sand-filter (sec Fig.
No. 4) located at the inlet to the storage tank or cistern will do this, but
they cannot be relied upon to remove bacteria. The cistern and the
sand-filter should be cleaned regularly, and they must be situated and
constructed so that the entry of surface water and possible pollution by
sewage, arc prevented.
Water storage tanks and cisterns should have covers that arc dust
proof and prevent the entry of light and animals. Overflow pipes should
be screened against the access of mosquitoes and other insects. The
outlet pipes should be about 2 inches above the bottom of the tanks and
the clean-out pipes flush with the bottom. There should be no connec
tion between cistern drains and sewage drains. Metal tanks arc commonly
used for storage above ground, where, if possible, they should be shaded
from the sun. As rainwater is soft and has a markedly corrosive effect on
iron, tanks of that metal should be well galvanised. For convenience
and economy masonry tanks are frequently built underground and that
helps to keep the stored water cool in the hot weather. Reinforced con
crete is the best material for underground tanks since it provides water
tight walls as well as the necessary structural strength. Masonry walls
must be carefully built, with strong cement mortar joints, and plastered
inside with two t inch coats of mortar (1 Portland cement: 3 sand) to
make them water-proof.
Surface Waters:—
Streams: In rural areas water from small streams draining isolated,
or uninhabited valleys (e.g. ravines in the jungle) may be of sufficiently
good chemical and bacteriological quality for human consumption in its
natural state. The intake may consist of submerged pipe protected by a
cage or a screen at the open end. It should be placed some distance from
the bank towards the centre of the flow and not too close to the bottom
of the stream. A small diversion dam may be required. In suitable
14
circumstances, the water may be gathered behind dams (see page 27)
into ponds and reservoirs but the area used for this purpose must have
a reasonably impermeable soil (e.g. various types of clay). At the time
of construction the area to be submerged should be cleared of vegetation
and decaying matter. Steps should also be taken to protect (by inter
cepting ditches, fences, hedges etc.) the environs of the reservoir and
the areas drained by its inflowing streams against surface washings,
human and animal pollution. The ponds so formed may become breed
ing places for mosquitoes and fresh-water snails (vectors of bilharzia),
so such schemes should not be undertaken without previously con
sulting the local medical authorities.
Though safe brooks of the type described above may be found in
sparsely populated areas, the waters of streams, rivers, ponds, etc., in
inhabited places arc so liable to pollution that they should be regarded
as dangerous for human consumption unless they are subjected to
purification. The kind of treatment necessary to render such waters
continually safe for domestic purposes is often impracticable for small
communities because of the expense involved and the standard of
supervision required.
Ground-water
Infiltration Galleries are really horizontal wells which collect water
over their entire length. In the case of large supplies they may be tunnels
which run into aquifer for varying distances from the main shaft of
the well. In rural areas they generally consist of open-jointed, 4-inch
(or larger) diameter pipes, surrounded by 6 inches or so of gravel, and
laid on the bottom of trenches which are deep enough to enter the water
bearing layer. After the pipes and gravel have been installed the
trenches are infilled. The latter type may also be used to collect water
from a scries of seepages or small springs. For this purpose the trenches
should be excavated a suitable distance uphill from the seepages and
springs and should follow the contours as the contours normally lie
across the flow of the water. By these means the water is gathered before
it appears on the surface. The pipes should slope to selected points
from which the water may be pumped.
In areas where the streams arc too liable to pollution for their
water to be used for domestic purposes without prior treatment it may
be possible to collect water from sand and gravel layers situated near
the streams. In these instances wells and/or infiltration galleries, are
constructed in the water-bearing layer, about 30 feet or more from the
banks of the stream. (See Fig. No. 5.) The water so obtained has usually
been adequately filtered through the sand before it enters the collecting
pipes but its purity should be checked by the necessary tests.
Springs: Provided the spring water has been filtered through at
least 10 feet of soil (though it may have acquired some chemical sub
stances on the way) it has usually been freed of harmful bacteria. (Care
must be taken not to mistake for a spring, the reappearance on the sur
15
face, of a stream that has gone underground for a short distance.) The
risk of contamination arises if the spring water is allowed to flow over
the ground before collection but the hazard may be eliminated by
gathering the water before it reaches the surface. This means digging
back into the hillside and placing a collecting tank on the impermeable
layer as illustrated in Fig. No. 5. Be careful not to dig through the
underlying impermeable layer as that is likely to let the water seep
downward and cause the loss of the spring. A diversion ditch should
be dug some 25 feet or more uphill and around the sides of the collect
ing point in order to intercept surface water before it can flow into, and
contaminate the spring. The soil from the ditch should be thrown up
on the downhill side so as to form a “bund" which increases the effect
iveness of the ditch. Putting a fence or thick prickly hedge on the bund
tends to prevent human trespassers.
The water from a number of small springs may be collected by the
method illustrated in Fig. No. 6, or by means of open-jointed agricul
tural pipcsina subsoil drain which follows the contour—a drain similar to
Fig. No. 5:—The method of collecting water from a spring
16
a small infiltration gallery. The pipes should slope towards one or
more points from which the water is conveyed to a collecting tank.
The area concerned should be protected against surface washings by
an intercepting ditch and bund, and against human and animal trespass
by a suitable hedge or fence.
Fig. No. 6 :—One method of collecting water from a number of
small springs
Wells : The common method of collecting ground-water is by
means of wells of which the main types are the hand-dug, the driven,
the jetted, the bore hole and the drilled. Irrespective of its type of
construction, a well which obtains its supply from the shallow ground
water (i.e. the water above the first impermeable layer) is called a shallow
17
tueli and one which draws from the deep ground-water (i.e. water below
the first impermeable layer) is referred to as a deep well. The terms
“shallow” and “deep”, as used in this connection, do not refer to the
actual depth of the well, and the shallow ground-water may be further
below the surface in some places than the deep ground-water is in other
parts. Most shallow wells are hand-dug, but some are jetted or driven.
Deep wells are generally drilled.
The Hand-dug Well: this is the commonest type of well in rural areas
throughout the world and it is usually the most suitable for small
communities. The equipment required for its construction is simple
and in most areas men accustomed to the work are to be found. The
majority of hand-dug wells are about 25 feet (7 metres) deep but depths
of 50 feet (15 metres) are not unusual, and occasional wells descend to
100 (30 metres) and more feet. The maximum depth for a hand-dug
well is considered to be 200 feet (60 metres), but the construction of
such wells is not free from danger to the workmen and it is advisable
to employ a trained supervisor, particularly for the deeper ones. Handdug wells are almost invariably circular in shape as that has great
advantages in economy and strength. The cost of lining a well varies
directly with its diameter but the diameter must be large enough to
allow room in which the men can do the excavating. The standard
diameter is between 3 and 4 feet and the latter allows sufficient space
for two sinkers to work together. Hand-dug wells act as reservoirs for
the water.
The usual way of constructing a shallow well is to excavate a hole of
the required diameter and depth and then to line it with masonry,
brickwork or concrete rings making sure that all the joints between the
stones, bricks or rings, for a deoth of at least 10 feet below ground level
are watertight. If the ground appears at all unstable the excavation
should proceed for 3 feet or so and the walls of the hole should then be
revetted with timber so to protect the workmen against caving of the
sides. The process of alternate digging and revetting the excavation
should then proceed to the required depth. Sometimes the permanent
lining is installed in similar stages, each section being held in position
by pins and curbs, or the lining is built in sections above its final level
and each section is sunk as a completed unit towards its final position,
as the excavation proceeds. Generally a combination of these methods
is employed.
Sanitary Precautions: It is most important that the location and the
design of the well are such as to afford to its water the greatest possible
protection against contamination. For this purpose the well should
possess the following features (see Fig. 7):— (i) It should be situated on
adequately drained ground which is above flood level and at least
100 feet, preferably uphill, from all potential sources of pollution.
(ii)
The well should have a watertight lining (e.g. concrete, or
18
Fig. No. 7 :—The features of a hand-dug well
tight-jointed bricks or stones), which may be improved by filling in the
space between the lining and the surrounding earth with puddled clay,
or concrete. In the case of shallow wells this lining should reach down
wards into the water-bearing layer, or to at least 10 feet (3 metres)
below the surface of the ground. The lining should be continued
above the ground (1 foot (30 ems) or more) and be surrounded at
ground level by a 6 foot (2 metres) wide watertight apron which is
sloped to a perimeter drain that carries the waste water away from
the well. The lining and the apron ensure that surface water can enter
the well only after it has been filtered through at least 12 feet (2 metres)
of soil. In the case of deep wells the lining should continue into the first
impermeable layer so that water cannot enter the well above that layer.
(iii) The well cover should be watertight and dustproof and its
upper surface should slope downwards and outwards from the centre.
(iv) The water should be drawn, preferably by a pump that is
self-priming, as that avoids the risk of the well being polluted by
extraneous water used for priming. Pumps which have their cylinders
above ground are cheaper to buy and easier to maintain than those
with their cylinders in the well.
19
(v) A well on sloping ground should be protected by an inter
cepting contour ditch situated about 50 feet (15 metres) uphill from
the well.
Before putting a well into use the water, the pump and the suction
pipe should be disinfected bv super-chlorination. (For method see page 37.)
N.B. Though pumps are capable of forcing water up pipes for
variable distances (depending on their power, and other factors)
they arc incapable of sucking water upwards for much more than
20 feet (6 metres). Pumps must, therefore, be located less than
20 feet (6 metres) above the water. Where the water does not
reach to within that distance of the surface the pump must be
lowered into the well for requisite depth.
Driven Wells
In areas where ground-water is available about 15 feet (4-5 metres)
or 30 feet (9 metres) below the surface and the intervening soil is neither
rocky nor unduly hard, driven wells have proved both efficient and
popular. Such wells are constructed by driving into the water-bearing
stratum, by means of a hammer or driving monkey, a screened well
point to the upper end of which, as it descends, suitable lengths of pipe
are attached. The pipes are commonly 14 to 2 inches in diameter and it is
only rarely that the depth of such a well is as much as 50 feet. A small
hole, about 2 feet deep, is dug with a crowbar to start the well-point
on its downward path and it is essential to see that the pipe is main
tained in a vertical position during driving. The plumb line used
for checking this should also be lowered frequently into the pipe to
ascertain when water has been reached. After the water-bearing layer has
been entered it is advisable to continue driving as the deeper this layer
is penetrated the less likely is the well to dry up. The pump should then
be attached to the upper end of the pipe, the pipe should be filled with
clean water and pumping should be started. At first the water
obtained will be muddy but it will usually clear after an hour or so of
vigorous pumping. Such pumping will remove the sand and fine earth
from the vicinity of the well-point and so “open” the aquifer—a pro
cedure necessarv to ensure a steady supply of water. The process may
be assisted by stopping the pump for a moment thus causing the water
in the pipe to fall suddenly and to pour out through the well-point
disturbing the fine particles surrounding the pipe. Pumping should be
recommenced immediately, and the process repeated several times till
the water is clear.
The pipe should be withdrawn if, by mistake, it has been driven
beyond the water-bearing stratum. If driving is obstructed by boulders,
or no water obtained at a suitable depth, the pipe should be lifted out of
the ground and put down in another place. This may be done by using
a crowbar, or wooden beam placed across a log or trestle, as a lever.
20
Once the water from the well becomes clear, a concrete platform
with a 6 foot radius sloping to a surrounding drain, should be built
around the pipe at ground level. The junction of the platform with the
pipe should be sealed so that surface water cannot trickle down along
side the pipe. This is best done by employing a pump with a base that
is wide enough to cover the hole completely. (Sec Fig. No. 8.) The
pump should be firmly fixed so that it does not move the pipe during
pumping. It is a common practice to withdraw the pipe and point used
in driving the well once the flow of water is established, and to replace it
with new piping and new screened well-point before sealing the top of
the well.
Most of these wells are fitted with suction pumps, usually of the
pitcher-spout type. The risk of contamination by priming may be avoided
by installing a well-casing of sufficient diameter to permit the pump
cylinder being immersed in the water. The plunger is attached by a
long rod to the pump handle. Before putting it into use the well and its
fittings should be disinfected. This is done by pouring down the well
a solution of chloride of lime (prepared as follows : — Mix 3 ozs of
chloride of lime containing 25% available chlorine into a watery paste
and then add sufficient water to make the mixture up to 5 gallons :
stir thoroughly and allow to stand: use the clear liquid and discard
the inert material that has settled to the bottom of the container).
Operate the pump till the water discharged to waste smells distinctly
of chlorine. Repeat this procedure a few times at intervals of one hour
and then allow the chlorine solution to remain in the well for 12 hours.
At the end of that time pump water to waste till it is free of the odour of
chlorine.
The purpose of the screened well-point is to allow ground-water to
enter the pipe freely but to exclude sand. A suitable size of opening for
the screen may be determined by passing sand from the water-bearing
stratum through sieves of known size. Once the screen deteriorates the
well-point must be withdrawn and replaced by a new one. It is,
therefore, advisable to select a screen of good quality metal that will last
as long as possible.
Jetted Wells: where plenty of water is available a good method of
sinking a well is by jetting. This process consists of inserting into the
ground a pipe tipped with a steel cutter and rotating this pipe while
water is pumped into its upper end. Under these conditions the pipe
descends into the soil and the water washes out of the hole the earth
loosened by the cutter. Wells with a diameter of about 1A inches are
easily made by this method. Where the soil is suitable, and the necessary
amount of water is available, wells with diameters of 10 to 15 inches
may be sunk to a depth of 300 feet, by jetting, but for the construction
of these bigger wells it is advisable to employ an engineer trained in
the work.
21
6 feet
4in.
U8in.
In areas with relatively coarse sand, driven
wells can be an excellent and very cheap means
of obtaining water. They can be driven rapidly
and put into operation quickly. With proper
technique, this well can be developed to increase
its capacity.
Noto the watertight casing which
extends down to a minimum of 10-ft. below
ground surface.
(Reproduced from WHO Monograph Series No. 42)
Fig. No. S :—A driven well.
22
Tool for boring in top soil, clay, sandy clay, or formations that
arc not too hard or caving. Cutter (a) may bo added to
permit boring up to 3-in. wider than standard size.
B^Spiral auger
C= Regular club bit for breaking through hard formations,
loosening rock, and breaking soft rock.
D^Tool for boring in soft, wet, sandy soils.
A
(Reproduced from WHO Monograph Series No. 42)
Fig. No. 9 :—Various types of earth augers
The system of jetting small diameter wells as used in India has been
described by P. C. Bose. It has given excellent results and a summary
of the method (quoted from WHO’S Monograph Series No. +2:
“Water Supply for Rural Areas and Small Communities”) is given in
Appendix F.
Tlorc-holr. Wells: A simple method of sinking a small diameter well
of shallow depth is by means of an auger. The auger (see Fig. No. 9)
which is usually about 4 inches across is rotated by hand. It is advisable
to give it a start by digging the first 12 or so inches of the hole with a crow
bar. The shape of the spiral allows the earth loosened by the boring to
rise upwards, but from time to time the borer should be raised out of the
hole together with the loose soil. If rocks or other hard layers are
encountered the auger has to be removed and a new hole started else
where.
Once the water-bearing layer has been penetrated sufficiently the
necessary length of piping, tipped with a screened well-point or strainer,
is lowered into the hole; the pump is attached to its upper end; and the
well is “cleared” by pumping. The space between the pipe and the sides
23
of the hole is then packed with concrete or puddled clay to a minimum
depth of 10 feet, and the usual concrete platform constructed around
the well at ground level.
Drilled Well: A drilled well is made by one or another type of
special drilling machine and the hole is then lined with a suitable
(usually steel) casing. This method has the advantage that it can reach
water-bearing strata farther below the surface than could be attained by
any other kind of well. As a rule the yields arc high, and unaffected by
droughts. The deep water is almost invariably free of pathogenic
bacteria but it often contains inorganic substances dissolved as it per
colated downwards.
The construction of a drilled well is a specialised task and should
be restricted to those experienced in the work. In the absence of local
geological data or previous drilling history in the area an attempt to
obtain water by this method is apt to be a gamble. It is expensive and is
generally beyond the means of small communities.
Cleaning of Wells: Open wells are very liable to become contamin
ated by dust. In dry, windy climates the dust entering a well may amount
to several inches in a year. Cleaning is therefore necessary, not only
to maintain the quality of the supply, but to ensure that the quantity
is not seriously reduced by dust or other foreign matter preventing
water gaining access to the well. In addition, small animals, e.g. frogs,
rats, are prone to commit suicide in wells in their anxiety to reach
water. Dug wells should be cleaned at least once a year and in dry
areas with much dust every six months.
The concrete or brick lining at the top of the well should first
be carefully examined, since if it has become loose it will make the
cleaning a dangerous operation for the cleaners. The inside of the
well may often be inspected by a shaft of light reflected from a mirror.
A lighted candle should be lowered into the well to test for harmful
gases. Old wells, particularly if over 15 metres in depth, often contain
a high concentration of carbon dioxide. If the candle flickers or goes
out, it should be assumed that gas is present in a dangerous concentra
tion and the well must be ventilated. Any method of circulating air
will achieve this purpose, e.g. a bundle of leaves or grasses is lowered
into the well and quickly withdrawn, and repeated until the well is clear
of gas. A hand-operated centrifugal fan forcing air through flexible
canvas tubes is also effective.
24
PURIFICATION OF WATER UNDER RURAL
CONDITIONS
The purification of unsafe water requires some trained supervision
if it is to be done effectively. Such supervision is rarely available in the
villages and even on well-managed estates the procedure tends to be
neglected sooner or later. Under these circumstances every e.r'ort must be
made to obtain a source that provides a naturally wholesome water and
then to collect that water and protect it against pollution by the methods
already described. Thus, the necessity for treatment of the water may
be avoided, and the practical importance of managing this can hardly
be over-emphasised.
If the water needs treatment this should, if at all possible, be done
for the whole community and certainly before, or on entry to the dwelling
so that the water from all the taps in the house is safe. The practice,
common in the tropics, of disinfecting (by filtration and boiling) only
the water to be used for drinking, teeth-cleaning, etc., though efficient
in itself (when carefully done) is frequently nullified by the servants
who, the moment the householder’s back is turned, are liable to fill the
carafes from the nearest tap rather than go some distance to collect
the safe water. Children are also likely to use the water from any tap.
Contrary to an all too common opinion, ordinary freezing of water,
though it may retard the multiplication of bacteria does not kill them,
and ice from a household refrigerator is no safer than the water from
which it was made.
Where some purification is required it should be confined to one or
more of such processes, as plain sedimentation, aeration, filtration and
sterilisation.
Sedimentation.
To accomplish sedimentation it is necessary’ to
retain the water for a time but the tank or reservoir used for this purpose
also provides storage and that assists in the maintenance of a continuous
supply'. Dangerous intestinal bacteria in water are gradually reduced in
numbers during storage, as conditions are not favourable to their
multiplication. Holding of the water allows suspended solids to settle
to the bottom and in doing so the solids carry many of the bacteria
with them. It requires 6 or more days (depending on the degree of the
initial contamination) to produce a marked reduction in the numbers of
bacteria and the cysts of amoebic dysentery may persist in water for 10
to 30 days. The solids settle at a rate which is largely related to their
particulate sizes ; e.g. coarse sand will settle quickly but fine clays and
silts need several hours. The time necessary for sedimentation may be
reduced to hours by adding a coagulant (e.g. alum or alumina ferric—
2| grains per gallon of water=l lb. to 2,800 galls.) manually or auto
matically, to still or slowly moving water by means of special apparatus
(sec Fig. No. 10). This process requires supervision.
25
(By kind permission of Jewell Filter Co. Ltd.)
Fig. No. 10 :—One type of micro-feed apparatus for adding
chemicals (e.g. alumina ferric, chlorine, etc.) to water
26
The type of settling basin most practicable for rural conditions is that
formed by constructing a simple earth dam across a suitable and pro
tected ravine. Such a basin also serves as storage for the water. The
velocity of the water should be reduced on entry to the tank and it should
be uniformally distributed across it. Earthen or wooden baffles may
assist in this. Cleaning and repairing of the basin is facilitated if it can be
divided into two sections each of which can operate independently of
the other.
The construction of a dam is not the simple matter it often appears
to be and if the proposed structure is to be other than small it is advis
able to obtain the services of an engineer experienced in the particular
work. Even for the smaller dams some knowledge of the basic principles
of siting and design are required. It is necessary beforehand to make
sure that the soil of the selected basin is sufficiently impermeable to
prevent the water soaking away; that the catchment area is large enough
to provide the required amount of water; and that the strength of the
dam is more than adequate to support the weight of water behind it.
A badly built concrete dam may collapse suddenly, and an earthen bank
often goes rapidly once it is breached.
The commonest cause of breakdown of an earth dam is the flowing
of waler over the top of the dam (unless this is sufficiently protected by
concrete) due to inadequate provision for the diversion of excess water,
more particularly the flow that follows heavy rain. This occurrence is
to be prevented by the construction of proper spillways clear of the dam
itself (see Fig. No. 11). Spillways should be cut out of solid ground
and their inverts should be well below the level of the top of the dam.
It is sometimes safer to make two spillways, one at each end of the dam.
.Another common cause of failure is faulty construction and under
mining of the embankment. The dam must have a base wide enough to
provide a slope of not less than 1 in 3 on the upstream side of the embank
ment and 1 in 2 on the downstream side. In building up an earth dam
three fundamental rules must be observed:—(1) The material (best
is clayey containing some sand) must be spread in continuous shallow
layers (4 ins. to 6 ins. deep) over the whole area; (2) it must be kept damp
(enough to retain a foot-print) but not too wet; and (3) each layer must
be well compacted before the next layer is added. (For fuller details
the reader is referred to standard books on this subject, and to Annex 7
of WHO Monograph Scries No. 42.)
Aeration. Aeration can be accomplished by allowing the water to
cascade over some rough concrete steps. Alternately, where the necessary
head is available, the water may be sprayed into the air from nozzles and
drained back into a tank in thin sheets over a rough concrete apron.
Aeration is commonly employed to eliminate odours (more
particularly those due to hydrogen sulphide) and to oxidise iron and
manganese salts. Aeration is also used for ridding the water of excessive
amounts of carbon dioxide which, when present, cause water to attack
any iron exposed in the distribution system.
27
co
28
Fig. No. 12 :—Section of a slow sand filter. Note that the outlet is
situated above the level of the filter bed.
Filtration. Filtration through sand as a method of purification of
water has stood the test of time. It may reduce the bacterial content of
the water by 85% to 99%. The two types of filter in common use in
community water supplies are the slow sand filter and the rapid (or
pressure) filter. Household filters are described on pages 43 and 44.
The slow sand filter requires little operational and maintenance skill
but it does need a certain amount of attention regularly. If it is neglected
it is liable to become a breeding ground for bacteria and a source of
contamination of the water. In urban supplies the filters are under
constant skilled supervision but experience has shown that in rural areas
the filters are far too often overlooked, especially if they are any distance
from the houses. This difficulty may be overcome in the case of villages
by appointing a particular resident to be responsible for the filter and
arranging for the local sanitary officer to inspect it at stated intervals.
A slow filter consists of a masonry tank containing 30 to 40 inches
(75 cm. to 1 metre) of fine sand, resting on a layer of shingle about
12 inches (30 cm.) deep. Below the shingle (on the floor of the tank),
are underdrains (open-jointed pipes or tiles) which collect the filtered
water and lead it to the outlet. (3ee Fig. No. 12.) Filters of this type
usually work with about 4 to 5 feet (1 to 1-5 metres) depth of water
on top of the sand and the water should percolate through at approxi
mately 2 gallons per square foot of filter surface per hour: i.e. a filter
bed of 10 ft. X 10 ft. (3 m. X 3 m.) could deal with some 5,000 gallons
of water during 24 hours.
In the upper 1 to 3 inches of the sand an organic material (known as
“zoogloea”) collects and this greatly improves the efficiency of the
filtration. The sand of the filter should be kept covered with water
29
so as to help maintain this biological layer. To prevent the water falling
too low the outlet of the filter is usually located 2 feet or so above the
level of the top of the sand (see Fig. No. 12). This matter needs
attention especially when the filter is being used intermittently. As
time goes on the zoogloea increases in quantity till it is sufficient to
retard the flow of the water unduly. When that happens the top 1 to
3 inches of sand should be scraped off. After it has been washed this
sand may be used again or fresh sand may be employed.
The raw water going on to the filter should be sufficiently clear to
permit seeing a silver coin held on edge between the fingers at least 10
inches below the surface (i.e. with a turbidity less than 40 parts per
million, approximately). If the coin cannot be seen at that depth the
turbidity must be reduced by passing the water through a settlement
basin before it enters the filter. Failure to do this will result in the filter
becoming clogged and useless after too short a period (which varies
with the degree of turbidity). It has then to be cleaned and restored
before being put into service again.
Rapid Sand Fillers:—For effective rapid filtration pretreatment of
the raw water is generally necessary. This treatment consists of adding
to the water, before it passes on to the filter bed, a coagulant, such as
alum or alumino-ferric, which forms a gelatinous precipitate, or
“floc”, that enmeshes the suspended solids and bacteria. This pre
liminary “chemical filtration” assists the rapid passage and improves
the standard of the filtrate.
There are two types of rapid sand filter, namely the open gravity
filter and the closed pressure filter. In the former the filtering material
is contained in an open concrete box and the water passes through it by
gravity'. Such filters often form part of urban purification plants but
they require more competent supervision than the ordinary small
community can afford.
In the pressure filter the filtering medium is enclosed in a sealed
metal drum to which the water is introduced under pressure. If the
turbidity of the raw water is less than 40 parts per million (see above)
the pretreatment may be carried out in the drum, but where the tur
bidity is greater than this the filter alone is not sufficient to ensure
complete removal of suspended solids, and in such cases the water must
be clarified before entering the filter. These filters also require com
petent supervision, but of a standard that is available on most plantations.
The usual rate at which pressure filters work is 80 to 100 gallons of
water per square foot of filtering surface per hour, but they may cope
with more than that if the character of the raw water permits.
These pressure filters can work under a maximum pressure of
100 lbs. per square inch, but it is usual to employ a much lower pressure.
The minimum pressure recommended is about 12 to 17 lbs. per square
inch (i.e. with a head of 30 to 40 feet). If the supply system has a fall of
less than this minimum it is necessary to provide the required head by
means of a pump. These filters are cleaned by first blowing air through
30
the dirty sand and then “back-washing”, i.e. passing water in the
reverse direction (from bottom to top) through the filtering medium,
and so washing away the impurities that were held up by the upper
part of the sand, and leaving the medium clean and ready for use. For
this purpose the water used should be filtered water (so as not to con
taminate the lower part of the filter) and it should be under a pressure
head of 25 to 30ft. Back-washing may be required daily (or at longer
intervals depending on the conditions of the new raw water) and the
wash water with its load of impurities must be run to waste. Allow
ance for this must be made in calculating the total amount of water
required. A typical layout of a pressure filter system is illustrated in Fig.
No. 14.
’
In filtration the filter consists of a “candle” constructed of metal
washers, kept separate by small bosses on their surfaces (e.g. the
Metafilter (see Fig. No. 15), or of spirally wound wire on a hollow
core (e.g. the Stellar filter, see Fig. No. 16). One or more of these
31
(By kind permission of Jewell Filter Co. Ltd.)
Fig. No. 14 :—A typical layout of a pressure filter and overhead storage tank
from which the water for back-washing the filter is obtained
candles are contained in a glass or metal cylinder, into which certain
amounts of diatomaceous earth (Kieselguhr) arc introduced. The raw
water is then run into the cylinder under pressure and as it escapes into
the candle it carries the diatomaceous earth and deposits it as a coating
on the outer surface of the washers or wire. So long as the necessary
pressure of water is maintained the diatomaceous earth forms a highly
effective filtering layer on the candle. The first water discharged from
the filter should be run to waste till it comes clear.
As filtration proceeds the slime and dirt extracted from the water
are retained on the surface of the diatomite till eventually the pressure
required to force the water through becomes excessive and the flow
diminishes to a uselessly low rate. When this occurs filtered water should
be sent the reverse way through the candles. This causes the diatomite
layer to fall off the candle to the bottom of the cylinder. The filtering may
then be resumed (running the first water to waste as before). It is possible
to repeat this procedure a number of times, but sooner or later the re
used diatomite must be discarded by back-washing it out of the filter unit
through the sludge valve in the bottom of the cylinder. When the waste
runs clear the valve is closed; a fresh quantity of diatomite is introduced
and the filter restarted.
32
The candles are mounted
in batteries in the cylinders and
their number depends on the
L
amount of water and rate of
filtration required. Filters of
this type are used by the
Services (especially on the
standard water carts) and they
arc made in various sizes cap
able of filtering from 25 (i.c.
for domestic filter) to 16,000
gallons per hour. Larger sizes
may be made or units can be
worked in parallel.
The makers claim that
Mctafiltcrs, without the help of
their Kieselguhr filter beds, will
Details of
filter out particles down to
Candle
0-0001 inches. They supply
Metal support.
Series of metal
Kieselguhrs with textures of
rings between
three different sizes which they
which water can
pass into the
call Metasil A, B and C.
hollow core.
Metal gauze fitting
Metasil A is relatively open and
a Inlet.
over rings.
will pass liquid through rapidly.
c Outlet.
Deposit of powder
Filter candle.
on both sides of the
Hollow meta
It is a fine filtering medium but
D glass
gauze, forming the
cylinder.
filtering medium.
not quite fine enough to remove
e, Impurities drain.
Fig. No. 15 :—
bacteria completely. Metasil B
Section of a Metafilter*
has smaller particles and when
a filter bed of this grade is used a filtrate free of bacteria, but not viruses,
is produced. Metasil C is finer still and slower filtering. The company
also produces “Metasil ALAG” in which a silver coating has been given
to the Kieselguhr particles (somewhat similar to the Sterasyl and
Katadyn filters—see below). The silver disinfects the water and prevents
the growth of bacteria in the filter bed. There are several other varieties
of Metasil.
The Katadyn Filter] : consists of one or more ceramic filter candles
(sec Fig. No. 17), the hollow cores of which have been filled with sand
that has been impregnated with activated silver (known as “Katadyn”).
The water is filtered through the candles and the sand and in the
process takes up minute quantities of the silver. This silver has bac
tericidal properties in clear water and the disinfecting power remains on
storage, provided the water contains, as suspended or colloidal matter,
no sulphides, no iodine in excess of 0-05 ppm, no chlorides in excess of
25 to 40 ppm and is not hard. The water is thus filtered and disinfected
in one process. Katadyn filters are made in different sizes that contain
from one to thirty candles and, depending upon the water pressure,
♦Obtainable from Paterson Candy International Ltd.
tObtainable from Messrs. C. M. Wales, Ltd.
33
are capable of dealing with 15 to 1,000 gallons per hour. With normal
usage Katadyn filter candles will last for 2 years.
The Stcrasyl (made by Bcrkefcld) and the Katadyn domestic
filters contain activated silver which makes them self-sterilising so
they do not require boiling.
All the impurities that arc filtered from the water arc deposited on
the outside of the candles. Regular cleaning of the candles with a soft
brush or cloth is, therefore, required, and care must be taken when re
moving the cylinder to sec that the candles arc not bumped and cracked.
The makers claim that “for all normal purposes the effective life of a
candle is from two to five years”.
Disinfection
There are a number of methods used for disinfection of water sup
plies, c.g. chlorination, silver treatment, ultra-violet radiation, etc. What
ever method is employed it should be the last stage, or the finishing
process, in the purification, before the water is distributed.
The filter
candle
Outlet
(filtered
Details of
Candle
■ Glass cylinder
A.
A continuoui coil of monel metal
wire wound on a fluted cylindrical
metal former ; 1 /2,000-inch gaps
between strand* permit passage of
water to the central core.
B.
Deposit of powder on to monel
wire.forming the filtering medium.
Inlet
(raw water)
Fig. No. 16 :—Section of a Stellar Filter.*
•Obtainable from Paterson Candy International Ltd.
34
Chlorination : The most com
monly used method of disinfecting
communal water supplies is chlorin
ation. It is most effective when the
A layer of silver quartz
water is reasonably bright and clear.
(i.c. Katadyn) between
There arc a number of ways of
applying chlorine to water and
various types of equipment for this
two layers of micropurpose may be purchased from
porous porcelain (the
any of the better known water
filtering medium)
engineering firms. One type is
illustrated in Fig. No. 10.
For small supplies the method
shotdd be simple and any appar
Silver quartz filling
atus which has tiny openings (that
arc liable to blockage), should be
avoided. In rural areas chlorine is
generally applied as a solution of
calcium hypochlorite (bleaching
Fig. No. 17 :—
powder). The amount of chlorine
Section of a Katadyn filter candle.
(by kind permission of Messrs. C. M. Wales)
available from ordinary bleaching
powder is 25% to 30% (this point should be carefully checked at the
time of purchase) but the powder is liable to lose some of its chlorine
during storage and on exposure to air. Stabilised forms of bleaching
powder (i.c. chlorinated lime with an excess of unslaked lime), however,
arc available (e.g. “Tropical Chloride of Lime” made by I.C.I.: “StaboChlor”: “Caporit”: etc.) and only such a type should be employed.
When chlorine is added to water it immediately combines with any
organic matter present in the water and the chlorine so deviated is not
available as a bactericide. It is, therefore, necessary to add sufficient
chlorine so that, after this combination has occurred, there will be ade
quate chlorine left (i.e. “residual chlorine”) to destroy the micro
organisms. Chlorine must be in contact with bacteria for some time if it
is to kill them and the amount of chlorine required for this has an inverse
relationship with the contact time. Thus the dosage of chlorine that
shotdd be applied to a particular water depends on the organic content
of that water and the time during which the chlorine will be in contact
with the germs.
A simple method of ascertaining the correct dosage of chlorine is
to make up a quantity of solution of bleaching powder of known strength
and to test it against the water to be treated. For example—10 grammes
(150 grains) of bleaching powder of 25% strength is dissolved in 5 litres
(8.79 pints) of water to give a stock solution containing available chlorine
500 parts per million (ppm) parts of water. One part of this stock solution
should be added to 100 parts of the water to be treated. This would give
a dosage of chlorine of □ ppm. If the chlorine residual after 30 minutes
contact were found (by means of the DPD test—see below) to be
greater than 0.5 ppm, the dosage should be reduced, and if less than
35
0.5 ppm the dosage should be increased. Once the dosage is deter
mined the required amount may be added to a known volume of
water to be retained in a tank for 30 minutes or it may be applied by a
drip feed adjusted to supply a certain amount of the chlorine solution,
within a certain time to a volume of moving water known to pass a
particular point in the same time.
Estimation of Free and Combined Residual Chlorine in I Vater.
Now that the Ortho-Tolidine test has had to be discontinued, a
suitable alternative is provided by the DPD method (Diethyl-pphcnylcne-diaminc sulphate), also known as p-amino-diethyl-anilinc
sulphate, first developed by Dr. Palin, and known as the Palin-DPD
method.
The reagent can be bought in a pure form, and in conjunction
with potassium iodide, can be used to estimate the concentration of
“free” chlorine (i.e. hypochlorus acid and hyposulphite ion), mono
chloramine (NHoCl) and dichloramine (NHCL) in successive stages.
The reagent produces a red colour with “free” chlorine (and also with
chlorine dioxide), but gives no colour with chloramines until potassium
iodide is added. The monochloramine releases free iodine from potas
sium iodide and the iodine gives the same colour as the equivalent
concentration of chlorine combined with chloramine. (Both intensity
and colour are identical.) An excess of KI is required to release iodine
from dichloramine, but otherwise the reaction is the same. For a small
user of the test, it is convenient to buy the compressed tablets sold for
for the test by BDH, and for measuring the colour developed, standard
discs arc also available for use in both the Lovibond Ncsslcriser and
the Lovibond Comparator.
Tablets
No. 1 tablet contains DPD and complexing agent, etc. This tablet
gives a colour with free chlorine only.
No. 2 is a small tablet containing a limited quantity of KI. Iodine
is released from monochloramine only. Thus tablets 1 and 2 together
give Free and monochloramine or separately Free followed by mono
chloramine.
No. 3 tablet is a larger KI tablet which releases iodine from di
chloramine (also nitrogen trichloride).
Thus tablets 1 and 3 give a total chlorine content. Tablet 1 followed
by 2 followed by 3 give separately the quantities of free chlorine; free
chlorine and monochloraminc; free chlorine and monochloramine and
dichloramine.
Discs for measuring the intensity of colour produced are:—
For Comparator (10 ml samples):
Disc 3/40 A Range 0-1.0 in 9 steps
Discs 3/40 B Range 0-4.0 in 9 steps
For Nessleriser 50 ml samples:
NDP 0.05 to 0.50.
36
Residual chlorine present in the strength of 0.5 parts per million
parts of water after thirty minutes contact, though a somewhat high
dose, is usually advisable to ensure adequate disinfection under rural
conditions. The cercariae of schistosoma are killed during thirty minutes
contact with 0.5 to 0.6 ppm residual chlorine but 2.0 ppm for the
same contact time mav be required to destroy the cysts of amoebic dysent
ery. Chlorine in such a dosage wotdd give the water a chlorinous taste
and make dechlorination (sec below) necessary. Filtration is a much
better and safer method of preventing the waterborne infection with
these cysts.
Super-chlorination consists in the application of a dose of chlorine
which considerably exceeds that required to disinfect the water. After
a suitable contact time the water is dechlorinated. It is the process to
use for single applications, e.g. in an emergency; after completing or
repairing a well and before putting it into use, etc.
The method is as follows :—To supcr-chlorinate use J oz. of 25%
stabilised bleaching powder to every 100 gallons of water to be
treated (i.e. an application of chlorine at 10 ppm). Weigh out the
required amount of powder, mix to a cream with some water and
then dilute with more water to one bucketful. Add the bucketful
of solution to the water, preferably while the tank etc. is filling;
stirring during the addition: allow 5 to 10 minutes contact period and
then dechlorinate by adding sodium thiosulphate crystals (dissolved
in a bucket of water) at the rate of J oz. of crystals to every
100 gallons of water. Stir the treated water thoroughly.
(Note: To ascertain the amount of water to be treated in a well etc. see
Appendix E)
For removing green growth and slime from the walls of the tanks
apply a solution containing J lb. of 25% stabilised bleaching powder in
3 gallons of water. After a few minutes contact scrub the surface
thoroughly and finally swill with water.
Disinfection by Silver
The purifying effect of silver on water has been known for centuries
and it imparts no unpleasant taste to the water. The water to be treated
must be clear (if necessary by prior sedimentation and filtration) and
aeration helps the disinfection. Deviation of a portion of the silver occurs
in the presence of chlorides, iron, hydrogen sulphide, or organic matter.
The bactericidal properties of activated silver (Katadyn) were de
monstrated by Krause in 1929 and arc used in the Katadyn filters (see
Fig. No. 17; and in the Elcctro-Katadyn Water Sterilizing Units.*
The Unit consists of a cylindrical chamber holding a number of
silver electrodes. The water goes through the chamber while a feeble
direct current passes between the electrodes carrying silver ions into the
•Obtainable from the Katadyn Filter Co., Zurich ; and from
C. M. Wales Ltd., Piltdown Lodge, Piltdown, Uckfield, Sussex.
37
water. The water is then retained in a storage tank for the required
contact time (about 1 to 12 hours). The action continues so that the
treated water is bactericidal and capable of disinfecting a further quantity
of water (up to three-quarters of the original amount which may be
added to it). Used in this way these Units will disinfect between 14,000
gallons and 1,440,000 gallons a day.
F
Fig. No. 18 :—An electro-silver water steriliser designed at the Tea Research
Institute, Assam. The graduated slot and the rate of flow determine
the depth that the silver electrodes are immersed in the water.
38
The bacteriologists of the Tea Research Institute, Tocklai, Assam
as the result of their experience during the construction of the Assam/
China Road in 1942-45 devised a purification plant suitable for use on
Tea Estates (see I.T.A. Memorandum No. 18 “Purification of Tea
Estates’ Water Supplies” : May 1947). In this plant the water is sprayed
(aerated) into a series of three settling tanks. (Ahimino-ferric, approx
imately 1 lb. to 5,000 gallons may be added if necessary.) From the
settling tanks the water passes through a slow sand filter, then through
a home-made electro-silver sterilisation unit. (Sec Fig. No. 18).
Fig. No. 19 :—Domestic pressure filters containing single Sterasyl filter
candles. The pressure may be supplied by the mains,
by a pump, or by gravity, but should not be less than
lOlbs. per square "inch (i.e. 23 feet head of water, approx),
preferably 40 lbs. per sq. in. Filters with n number of
candles for larger supplies are available.
(By kind permission of British Berkefeld Filters Ltd.)
39
This plant has proved effective and is usually adjusted to deal with 300
to 350 gallons of water an hour, or approximately 8,000 gallons in 24
hours.
Removal of Iron and Manganese.
Iron is present in most soils, and nearly all ground-waters, as they
percolate through the earth, acquire some iron, though it may be only a
minute quantity. Surface waters may also be affected. Manganese
usually accompanies the iron but in smaller amounts. Waters that contain
more than a trace of iron (0.3 parts per million is permissible but 1 part,
or more, per million is excessive), have a flat metallic taste, and are
undesirable for laundry or culinary uses (e.g. the iron combines with
the tannin in tea to give the infusion an inky colour). When present
even in traces the iron tends to accumulate in the pipes of a distribution
system. That generally leads to the growth of “iron bacteria” which
accentuate the undesirable taste and colour of the water and increase the
tendency to blockage of the pipes. Ferruginous waters are unsuitable
for boilers and for many industrial processes.
Iron is usually present in water in solution as ferrous bicarbonate
(occasionally as higher oxides or in complex organic combinations).
The exposure of such water to the air changes the soluble ferrous
bicarbonate into the insoluble ferric hydroxide, which appears as an
opalescence and then as a brown deposit. This reaction is utilised to
free water of iron and the usual processes of open storage and filtration
will remove the traces of iron present in most waters. Where this is
inadequate the water should be aerated (see page 27), and the insoluble
iron allowed to settle to the bottom of a storage tank, helped, if necessary,
by the addition of a coagulant such as alumino-ferric (24 grains per
gallon of water). The water may then be filtered, but if most of the iron
is not removed before filtration it is apt to cause blockage of the filters.
In some cases these methods arc not sufficient and more comp
licated treatment, including the use of chemicals, may be required.
Chlorination assists in precipitating iron from the water, and the ‘lime’
process of softening water is also effective in extracting iron. Before
embarking on such processes, however, it is wise to obtain the advice of
water engineers or chemists.
Special pressure filters designed to remove iron and manganese from
water are obtainable from the leading water engineering companies.
In these filters there is a layer of hard, dark, granular, sand-like substance
on top of the sand-bed, and as the water passes through this layer the
desired chemical change occurs. The insoluble iron is then extracted as
the water continues through the ordinary filtering medium, and is
discharged from the filter during back washing. Filters of this type
have proved efficient on certain tea estates in Assam.
40
Hardness. Hardness, or the soap-destroying property, of certain
waters is most undesirable for such waters not only form an insoluble
curd with soap but deposit lime-scale (“fur”) in boilers and hot water
systems. Hardness has little or no effect on synthetic detergents so the
need for household water-softeners has been reduced. If the hardness
is removed by boiling it is known as “temporary hardness” and it is
due to the presence in solution in the water of the bicarbonates of
calcium and magnesium. These substances arc reduced by heat (160°F,
or more) to the insoluble carbonates and precipitated out of the water.
If the hardness docs not disappear with boiling it is known as “perm
anent hardness” and is caused by the presence of sulphates, chlorides
or nitrates of calcium and magnesium which remain in solution in spite
of heat.
Of the methods of softening hard water the base-exchange process
is the most suitable for small supplies. In it the water is passed through
synthetic resins which have the power of absorbing calcium and
magnesium and replacing them with their equivalents of sodium.
This exchange takes place practically instantaneously but after a time
the supply of sodium becomes exhausted and the resins have to be re
generated by passing a solution of sodium chloride (i.c. brine) through
them. A typical water-softening plant consists of an enamelled cylinder
almost filled with resins. The raw water enters at one point, passes
through the resins, and is drawn off at another point entirely free of
hardening salts. Once the quantity of water with which the apparatus
can deal (this is usually marked on an attached meter) has passed through,
the required amount of common salt (or brine may be used) is added
through the top of the cylinder. The water on entry dissolves the salt,
carries it through the resins, depositing sodium and acquiring calcium and
magnesium on the way, and is then discarded. Though this inter
change takes only a few minutes it is necessary to continue running the
water to'waste till all the salt has been removed from the plant before
putting it into use again. Plants which are automatically regenerated by
brine from an adjacent cistern are also obtainable. (Sec Fig. No. 20.)
Removal of Salts. Sodium chloride and other salts may be removed
from water by “distillation” (i.e. by boiling the water and condens
ing the steam in a still) or by “artificial distillation” (an ion-exchange
process), but both methods arc so expensive as to be practicable only in
special eases and/or for limited amounts of water (e.g. drinking water
only; water for boilers; etc.) It is usually better to obtain another,
salt-free source of supply, where that is possible. Small ion-exchange
plants, capable of providing a few gallons of fresh water from salt water
daily and suitable for individual dwellings are obtainable and bigger sets
are made by most of the water-engineering firms (e.g. Paterson Candy
International Ltd.).
41
(By kind permission of Permutit & Co. Ltd.)
Fig. No. 20 :—A domestic water softener
PURIFICATION OF WATER ON A DOMESTIC
OR INDIVIDUAL SCALE
The principal methods of purifying water on a small scale are, boil
ing, chemical disinfection and filtration. These methods may be used
singly or in combination but if more than liltration is needed the boiling
or chemical disinfection should be done last.
Disinfection.
Boiling is the most satisfactory way of destroying pathogenic organ
isms in water, and it is equally effective whether the water is clear or
cloudy, whether it is relatively pure or heavily contaminated with organic
matter. Boiling destroys all forms of disease-producing organisms
usually encountered in water, whether they be bacteria, viruses, spores,
cysts or ova. To be safe the water must be brought to a good “rolling”
boil (not just simmering) and kept there for some minutes. Boiling
drives out the gases dissolved in the water and gives it a flat taste, but
if the water is left for a few hours in a partly filled container, even though
the mouth of the container is covered, it will absorb air and lose its flat,
boiled taste. It is wise to store the water in the vessel in which it was
boiled. Avoid pouring the water from one receptacle to another with
the object of aerating or cooling it as that introduces a risk of re
contamination.
Chlorine is a good disinfectant for drinking water as it is effective
against the bacteria associated with water-borne disease. In its usual
doses, however, it is ineffective against the cysts of amoebic dysentery,
ova of worms, cercariae and organisms embedded in solid particles.
Chlorine is easiest to apply in the form of a solution and a useful
solution is one which contains 1% available chlorine, e.g. Milton
Antiseptic; (Dakin’s solution contains 0.5% available chlorine, and
42
bleaching powder holds 25% to 30% available chlorine). About 2J
tablcspoonfuls of bleaching powder dissolved in one quart of water will
give a 1% (approx.) chlorine solution. To chlorinate the water add 3
drops of 1% solution to each quart of water to be treated (2 tablespoon
fuls to 32 Imperial gallons), mix thoroughly and allow it to stand for
20 minutes or longer before using the water.
Chlorine may be obtained in tablet form as “Stcrotabs” (formerly
known as “Halazone”) and obtainable from Boots the Chemists, Ltd.
in the U.K.); the directions for use are on the packages.
Iodine is a first-class disinfecting agent and 2 drops of the ordinary
tincture of iodine are sufficient to treat 1 quart of water. Water that is
cloudy or muddy, or water that has a noticeable colour even when clear
is not suitable for disinfection by iodine. Filtering may render the water
fit for treatment with iodine. If the water is heavily polluted the dose
should be doubled. Though the higher dosage is harmless it will give
the water a medicinal taste. To remove any medicinal taste add 7%
solution of sodium thiosulphate in a quantity equal to the amount of
iodine added.
Iodine compounds for the disinfection of water have been put into
tablet form, c.g. “Potable Aqua Tablets” (obtainable from Frost Labor
atories, 430 Lexington St., Auburndale, Boston 66, Massachusetts);
full directions for use are given on the packages. These tablets are
among the most useful disinfection devices developed to date and they
arc effective against amoeba cysts, cercariae, leptospira and some of the
viruses.
Domestic Filters
There are two types of domestic filter in common use, viz. the sand
fdter and the candle filter. In the tropics the supervision of all domestic
filters should not be left to the servants. It is a task for the householder
himself or his wife.
A Household Sand Filter (see Fig. No. 4) is easily made with a steel
drum, sand and gravel, and though they cannot be relied upon (unless
operated with skill) to remove bacteria, they arc generally effective
against the larger organisms such as amoebic cysts, eggs of worms, etc.
The upper layer of the sand has to be removed periodically, and the filter,
if neglected, is liable to become a breeding place for bacteria. Sand filters
are, therefore, not recommended for ordinary domestic use. Household
Pressure Filters dealing with 1,800 gallons or more in the day are made by
he leading water-engineering firms. They are reliable, but like all filters,
require some attention, e.g. back-washing etc.
There are several types of candle filters but only those with fine
grained candles arc suitable for household purposes unless the water is
boiled or disinfected after filtration. Ceramic Filters with fine-grained
candles (e.g. Chamberland 1.2 and Selas 015) will remove pathogenic
bacteria but the}’ must be carefully examined at frequent intervals to
ensure that there are no cracks in the candles or leaks that would let the
water through without filtration. At least once a week the candles should
43
ll
be scrubbed with a grease-free brush and then boiled for 20 minutes.
This should also be done if the candle becomes coated or clogged.
Provided this care is taken the filtered water may be used without
boiling, or disinfection.
Another kind of candle filter employs Kieselguhr (diatomaceous
earth) as the filtering medium. Only the line-grained type should be
obtained. The Metafilter and Stellar filter (which have already been
described) are of this type and are available in sizes suitable for house
hold purposes. The Berkefeld* (sec Fig. No. 22) is another well-known
domestic filter using Kieselguhr candles.
Most leading manufacturers of water appliances make an apparatus
consisting of a filter candle housed in a casing to which a hand pump
and inlet and outlet lengths of hose arc attached (sec Fig. No. 21).
With such a unit a traveller may pump water from a stream or lake
through the filter into a suitable vessel. The apparatus, which is some
14 inches long and weighs about 7 pounds when packed for transport,
will filter approximately 15 to 25 gallons of water per hour. A smaller
and very much lighter type called “The New Traveller” is also available
(Fig. No. 21)*. If “silver” is incorporated in the candle (c.g. Katadyn,
Sterasvl, Metafiltcr, etc.) the water will not only be cleared of such
things as cysts, ova, ccrcariae and suspended matter but will also be
A
Fig. No. 21 :—Two types of portable filters suitable for
travellers, campers etc. They each use silver-impregnated
candles. The method of operating (a) is illustrated. To
operate (b) remove the cap, fill the container with the water,
screw the cap down tightly and pump for about 30 seconds.
(By kind permission of British Berkefeld Filters Ltd.)
•Obtainable from British Berkefeld Filters Ltd.
44
freed (after 20 minutes retention in a non-metal container) of pathogenic
bacteria (ree also page 33). These silver-impregnated candles are
self-serilising and do not need to be boiled.
In tests carried out at the London School of Hygiene and
Tropical Medicine, Professor Fulton added live Coxsackie virus to a
quantity of distilled water, and passed the water through a Sterasyl
filter candle. The filtrate was allowed to stand in a test tube at room
temperature for five minutes, when it was injected into mice, and
found to be non-infective. This result was most probably due to the
sterilising effect of the silver as the pores in the filter were too big to
hold back organisms as minute as viruses.
Household Water Containers : Where water has to be carried from
a well or standpipe it is the common practice to keep some water in the
house. Water that has been treated with chlorine, iodine or silver retains
some residual protection for a short time but water that has been purified
by boiling or filtering may be rccontaminatcd immediately. It is.
therefore, essential that the stored water be shielded against pollution.
The containers used for storage must be kept clean and regularly rinsed
with boiling water or washed out with a strong chloride of lime solution
(e.g. 1A ozs. to 5 gallons water) which is later removed by swilling
with wholesome water. The containers should have a cover which fits
closely enough to prevent the entry of insects, dust and other im
purities, and cups and other utensils should not be dipped in the water.
A container with a narrow neck is an advantage as it prevents this. The
water should be poured from the container or drawn off through a builtin tap or spigot.
Aerated Waters : There is a common belief that soda and other
aerated waters are safe, but this is true only if they have been made
with wholesome water and the necessary care against contamination
has been exercised during manufacture. In bottled water bacteria grad
ually decrease in numbers but the cysts of amoebic dysentery and ova
of certain parasites harmful to man may survive long storage. Carbon
dioxide acts on some bacteria only, so carbonated beverages arc not
necessarily safe.
Swimming Pools: Many estate and mine bungalows now have
bathing pools located in their compounds. The pools are generally small
and intended solely for the use of the family and a few friends. Though
many allegations of infections acquired from swimming pools are
ill-founded, there are undoubted risks where pools are inadequately
supervised. The main dangers are from human sources, but in countries
like Malaya there are also risks from animals, e.g. leptospirosis from
pollution of the water by rats etc.
Pools having a good natural flow of water through them can be
satisfactory but thej’ are only as safe as the water in them, and its safety
depends (as described in the preceding pages) upon its source and its
liability to pollution. The precautions already mentioned should be
carefully followed.
45
It is the general practice for the bungalow pool to be filled with clean
water and then to be emptied, cleansed and refilled at intervals of a
few days or even a few weeks. This method of “fill and empty” is not
by itself satisfactory as the sanitary standard of the water deteriorates
after a brief period of use. It should be reinforced by the periodical
addition to the pool water of a disinfectant. Disinfection by the
electro-silver method (see pp. 37 -40) is suitable, or chlorine may
be used. In the latter case 1 or. of stabilised bleaching powder is
required for every 1,000 gallons of water in the pool. The required
amount of bleaching powder is dissolved in cold water in a bucket.
After stirring thoroughly, allow it to settle and then apply the solution
as evenly as possible over the whole surface of the water in the pool.
This may be done by means of a watering can or a stirrup pump. The
disinfectant should be added to the fresh water and then applied each
evening when bathing for the day is finished. It is a good thing to check
the chlorination by taking samples of the water from a few places in the
pool half an hour after the application of the bleaching powder. The
amount of residual chlorine present in the water can then be tested with
the DPD reagent as described on page 36. There should be a residual
chlorine of at least 1 ppm and the amount of bleaching powder added
should be sufficient to ensure this concentration.
The “fill and empty” method, augmented by disinfection, is
suitable only for pools holding less than z0,000 gallons of water. For
pools with a capacity in excess of this it is preferable to install a con
tinuous circulation system with a filtration aeration and chlorination
plant as is done at all modern public swimming baths.
Fig. No. 22:—A domestic filter using Kieselguhr candles.
46
APPENDIX A
Chemical Standards for Drinking Water.
(«) (suggested by WHO Study Group). The following substances may
be present in the quantities designated “permissible” and the water
would be generally acceptable by consumers. Values greater than those
marked excessive would markedly impair the potability of the water.
Concentrations in parts per
million (i.e. mg per litre").
Substance
Total solids
Colour ...
Turbidity
Taste—unobjectionable
Odour — unobjectionable
Iron (Fe)
Manganese (Mn)
Copper (Cu)
Zinc (Zn)
Calcium (Ca)
Magnesium (Mg)
Sulphate (SO.])
Chloride (Cl)
Magnesium
Sodium Sulphate
Phenolic Substances (such as
Phenol)
*PIatinum Cobalt Scale.
Permissible
Excessive
500
5 units*
5 unitsf
1,500
50 units*
25 unitsf
0.3
0.1
1.0
5.0
75
50
200
200
500
1.0
0.5
1.5
15.0
200
150
400
600
1,000
0.001
0.002
fTurbidity Units.
for further details consult the standard works, e.g.
“Water Treatment and Examination”. Ed. W. S. Holden. Churchill: London, 1970.
“Standard Methods” by U.S. Public Health Association; etc.)
The water should be neutral or slightly alkaline (pH 7.0 to 8.5)
with a pH never less than pH 6.5 or more than pH 9.2.
Fluorides in concentrations of one part per million are quite safe
and markedly reduce the incidence of dental caries in the community.
Public Health Authorities recommend that waters with a lower content
than that should have sufficient sodium fluoride added to make the
concentration up to 1 ppm. Public supplies should not ordinarily
contain more than 1.5 ppm fluorides as effects, varying from slight
mottling of the teeth to more serious consequences, depending upon the
degree of excess, may occur.
Nitrates in excess of 50 parts per million (as NO3) may adversely
affect the red colouring matter of the blood (haemoglobin) in infants.
47
(i) There are a number of substances which are not harmful in
themselves but which are used as indicators of contamination. They are
all increased in the case of pollution of animal origin.
The usual upper limits are :—
Oxygen absorbed from permanganate
Albuminoid ammonia
...
...
Free and saline ammonia
...
Nitrites
...
...
...
...
2 parts per million
0.1 ppm.
0.05 ppm.
a trace
A rough guide is—if the albuminoid ammonia is as much as 0.08
parts per million the free and saline ammonia should not exceed 0.05
parts per million. In all sewage, and most sewage effluents, the free
ammonia exceeds the albuminoid ammonia. If pollution from human
sources can definitely be excluded higher values than those mentioned
may be allowed.
(c) (suggested by WHO Group). The following substances,
if present in drinking water in excess of the concentrations mentioned
would give rise to actual danger to health and would constitute grounds
for the rejection of the water for domestic purposes :—
.'1 laxiniuin allowable
concentration
Substance
0.1 parts per million
Lead (as Pb)
0.05 parts per million
Selenium (as Se) ...
0.2 parts per million
Arsenic (as As)
0.05 parts per million
Chromium (as Cr hexavalent)
0.01 parts per million
Cyanide (as CN)
APPENDIX B
Methods of Collecting Water Samples for
Chemical Examination
If the sample is taken from a standpipe, the water should be allowed
to run for a few minutes before drawing the sample. The mouth of the
pipe should be washed with running water. Allow the water to flow
slowly into the bottle, down the side, to avoid aeration.
A sample is obtained from a well by lowering a clean bucket into
the water and filling the bucket so as not to disturb the sediment at the
bottom of the well. The bottle is filled from the bucket by means of a
clean cup. New wells should be allowed to settle before taking samples.
Samples should be collected in a thoroughly clean Winchester
Quart bottle (about A gallon) but if that is not available use one or more
ordinary bottles capable of holding A gallon between them. The corks
and bottles should be clean. The bottle or bottles should be rinsed in the
water to be sampled and then filled up to the top, stopper inserted and
securely tied down.
48
If the water passes through cisterns, storage tanks or a system of
distributing pipes, it is better to take samples from the pipe as it is used
for consumption.
Fill the bottle under normal weather conditions, label dearly with
brief description of the water whether Well, Stream, Tank etc. and its
uses. Date and Time of collection of the samples should be stated. A
covering letter should give as much information as possible as to source
of supply, liability to pollution etc.
APPENDIX C
Bacteriological Standards for Drinking Water recommended
by the WHO Study Group
“Some public drinking-water supplies are chlorinated or otherwise
disinfected before being distributed; others arc not. Effective chlor
ination yields a water which is virtually free from coliform organisms
i.c. these organisms arc absent in 100-ml portions; if communal supplies
which arc distributed without treatment or disinfection cannot be main
tained to the bacteriological standard established for treated and dis
infected water, steps should be taken to institute chlorination or dis
infection, or other treatment, of these supplies.
“A standard demanding that coliform organisms be absent from
each 100-ml sample of water entering the distribution system—whether
the water be disinfected or naturally pure—and from at least 90% of the
samples taken from the distribution system can be applied in many parts
of the world. Although there is no doubt that this is a standard that
should be aimed at everywhere, there arc many areas in which the attain
ment of such a standard is not economically or technically practicable.
“In these circumstances there would appear to be economic and
technical reasons for establishing different bacteriological standards for
public water-supplies which arc treated or disinfected and for those
which arc not treated. The following bacteriological standards are
recommended for treated and untreated supplies for present use through
out the world, with the hope that improvements in economic and tech
nical resources will permit stricter standards to be adopted in the future.
“The standards described below arc based on the assumption that
frequent samples of water will be taken...For each individual sample,
coliform density is estimated in terms of the ‘most probable number
(M.P.N.)’ in 100-ml of water, or ‘MPN’ index... The use of the MPN
index is recommended as the basis of quantitative estimation of coliform
density after full recognition of its limitations. However, the value of
the index is sufficiently enhanced by the use of data from a series of
samples to warrant its use in the recommended standards.
"Treated water
“ In 90% of the samples examined throughout any year, coliform
bacteria shall not be detected or the MPN index of coliform micro49
organisms shall be less than 1.0 None of the samples shall have an MPN
index of coliform bacteria in excess of 10.
“An MPN index of S-10 should not occur in consecutive samples.
With the examination of five 10-ml portions of a sample, this would
preclude three of the five 10-ml portions (an MPN index of 9.2) being
positive in consecutive samples.
“In any instance in which two consecutive samples show an MPN
index of coliform bacteria in excess of S, an additional sample or samples
from the same sampling point should be examined without delay. This
is the minimum action that should be taken. It may also be desirable to
examine samples from several points in the distribution system and to
supplement these with samples collected from sources, reservoirs, pump
ing stations and treatment points. In addition, the operation of all treat
ment processes should be investigated immediately.
“Untreated water
“In 90% of the samples examined throughout any year, the MPN
index of coliform micro-organisms should be less than 10. None of the
samples should show an MPN index greater than 20.
“An MPN index of 15 or more should not be permitted in consec
utive samples. With the examination of five 10-ml portions of a sample,
this would preclude four of the five 10-ml portions (an MPN index of 16)
being positive in consecutive samples. If the MPN index is consistently
20 or greater, application of treatment to the water-supply should be
considered.
“In any instance in which two consecutive samples show an MPN
index of coliform organisms greater than 10, an additional sample or
samples from the same sampling point should be examined immediately.
It may also be desirable to examine samples from several points in the
distribution system and to supplement these with samples collected from
sources, reservoirs and pumping stations.
“When accurate and complete data concerning the sanitary con
ditions at the sources of an untreated water-supply, covering all possible
points of pollution, are available and indicate that indices higher than the
established maximum may bear little relation to potential health hazards,
the local health and water-supply authorities should be responsible for
ruling that such higher indices do not constitute need for treatment of
the water.”
50
APPENDIX D
Collection of Water Samples for Bacteriological
Examination
Samples of water should be collected and sent for examination
in sterilised glass stoppered bottles of approximately 280 ml. (about
1 pint) capacity.
If the sample of water to be examined is likely to contain traces of
chlorine this fact should be stated when applying to the laboratory
for the bottles, as bottles specially prepared for collecting such samples
have to be supplied.
If the sample will necessarily take more than three hours to reach
the laboratory it should be dispatched packed in ice (in an insulated
box if possible).
The best time to collect a sample of water is about 7.30 a.tn.
The sterile bottle should be opened only at the moment it is required
for filling with the sample of water.
Carefully remove the paper cap covering the mouth of the bottle.
Hold the bottle at the bottom, cautiously remove the stopper with the
other hand and hold it in the fingers until the bottle is filled. The stopper
should not be laid down or allowed to touch anything. When the bottle
is full replace the stopper, tie the paper cap round, label and despatch.
Collection of Water from a Tap: Remove any external fittings such as
anti-splash nozzle, rubber tubing, etc. Turn the tap on full and allow the
water to run to waste for two or three minutes. Then turn the tap off,
clean the outside with a clean dry cloth, flame the tap with a blow lamp or
a piece of cotton wool soaked in methylated spirits for two or three min
utes. Cool the tap by opening it and allowing the water to run to waste
for a few seconds, then fill the bottle with the water running gently, so as
to avoid splashing. Replace the stopper and paper cap, label and despatch.
Collection from a Stream, Lake, Reservoir, Spring, or Shallow Well:
Remove the paper cap and the stopper as described above. Hold
the bottle from the bottom and plunge it neck downwards to a depth
of about one foot below the surface of the water. The bottle should then
be rotated till the neck points slightly upwards, the mouth being directed
towards the current. If no current exists as in the case of a shallow well,
an artificial current should be created by moving the bottle horizontally.
When the bottle is completely full bring it up rapidly to the surface
and immediately re-stopper it. Care should be taken that no water enter
ing the bottle has previously come in contact with the hand. From a
stream, lake, etc., water should not be collected too near the bank or too
far away from the point of draw-off.
From a Deep Well fitted with a Hand Pump : The pump should
be operated for about five minutes before collecting the sample. The
51
13 7/
mouth of the pump is sterilised by means of a blow lamp or cotton wool
soaked in spirits as in the case of a tap. After sterilising the pump should
be worked again until seven or eight gallons of water run to waste. Col
lect the sample by allowing the water to flow directly into the bottle from
the pump.
From a Well without al’untp : Where the water has to be lifted up by
means of a pail. Sterilise the pail by means of a blow lamp or by filling it
up with boiling water and leaving it there for about ten minutes and then
emptying it completely. After sterilising the pail it should not be allowed
to touch the ground. Allow it to cool and lower it into the well without
touching the sides. Fill the pail with water at a depth of about one foot
from the surface, quickly withdraw it and fill the bottle. Care should be
taken not to contaminate the stopper with the fingers. Replace the stop
per and paper cap, label and despatch.
52
APPENDIX E
Estimation of Quantity of Water Available
The amount of water in a well may be ascertained by the use of the
following formula :—
D2 x W X 5 = Gallons of water
Where : D = Diameter of the well in feet
W = Depth of the water in feet
The amount of water in a full pipe, may be ascertained by the following
formula :—
G = D= 4- 30
Where : G = number of gallons per foot length of pipe
and
D = the internal diameter of the pipe in inches
The approximate amount of water that can be raised by means of a pump
may be determined by the following formula :—
G = d2 x L X 0.034 x S
in which G = gallons discharged per minute
d = diameter of the pump in inches
L = length of stroke in feet
0.034 = gallons contained in 1 foot of 1-inch pipe
S = strokes per minute
An allowance of at least 10% must be made for inefficiency of the
pump.
The approximate, amount of water which can be raised by a hydraulic ram
may be determined by the following formula :—■
G X II X c
g =-----------------h
in which G = gallons per hour passing through the ram
11 = head of water on the drive pipe
h = height in feet to which water is to be raised
c = efficiency of the ram
g = gallons per hour raised
The value of “e” varies considerably with different factors for
“H” and “h”, but averages about 60%
Head of Water and Pressure
1 foot head of water = 0.4331 lbs. per sq. inch pressure
1 pound per square inch pressure of water = 2.31 feet head
53
APPENDIX F
A Method of Jetting Small Diameter Wells
(as used in India, described by P. C. Bose)
(Copied from WHO Manuscript Series No. 42)
“Equipment :
(1) tripod bamboo with 25ft. of clearance
(2) hand-operated lift and force pump (double-acting, with
plunger 4 in. in diameter)
(3) 4 chain-type wrenches for gripping pipes
(4) 40 ft. of high quality hose, 1.1 in. diameter.
(5) casing pipe, boring pipe, a swivel joint, steel cutter, pulley
ropes, small hand tools.
The Jetting process :
(1) Dig a hole 5 ft. deep over which the tripod is mounted; this
gives a reasonable starting depth.
(2) Attach the cutter to one end of a 11 in. boring pipe, usually
about 20 ft. in length; swivel to other end and place cutter
end of pipe into the hole; suspend the pipe and swivel with
pulleys from the tripod. The swivel joint allows water to
enter the boring pipe from the hose while, at the same time,
permitting the boring pipe to revolve without leaking.
(3) The hose is attached to the force pump which pumps water
from a sump excavated in the ground near the well. (The
pump suction pipe must be held clear of the bottom and sides
to avoid sucking up mud and sand.)
(4) Jet-boring starts as the pumpers begin to force water into the
boring pipe, at which point the men with the chain wrenches
begin to turn the pipe.
(5) With the pressure of the water and the twisting action, the
bore pipe begins to descend, and the jetted water begins to
boil up around the sides of the bore pipe. This water is full
of suspended matter and is really light mud. (The more water
that can be pumped through the pipe, the faster it will descend
and the more and larger will be the suspended matter being washed
out of the hole.'} In a short time the first 20 ft. of pipe will be at
ground level. The swivel is removed; a second length
of bore pipe is screwed on; the swivel is attached to this
new length of pipe; and the pumping, jet-boring process
begins again.
(6) One after another, the bore pipes are sunk until the desired
depth is reached. This can be ascertained by examining the
borings that are coming out of the well. (In West Bengal the
water-oearing stratum is fairly fine sand with an effective
size of from 0.16 mm to 0.02 mm.) When this stratum is
reached boring is stopped; but pumping continues at that
level for some time to clean the whole well.
54
(7)
Jetting water is re-used by letting the dirt and sand settle out
in the sump.
Placing the Screen
(1) The entire column of jet-boring pipe is now removed and
the cutler is taken from the end of the bottom pipe.
(2) The well screen is now attached to the first length of well
pipe, and the process of lowering the pipe is repeated with
pumping, but through the screen. (Naturally there is little
resistance in the recently jetted hole.) The screen is open at
the bottom; and, w’hen it is in the position desired, a pre
seated plug is dropped into the pipe and closes the hole at the
bottom of the well screen, sealing the bottom of the well.
A well-point with a closed end may also be used, although
sometimes a few feet of hole may be lost while raising the
the jet and lowering the well-point.
At this stage of the process, when water is being pumped down
through the well pipe and screen, washed pebbles can be dropped into
the hole around the out-side of the well pipe. These are heavy enough
to settle against the upward stream of water, and the stream can be regu
lated to allow settlement. These pebbles of round, washed gravel,
about 1 /25th in. to 1 /5th in. in size help form a gravel pack around the
well, thus reducing the possibility that fine sand may get packed up
around the screen and enter the well, with a consequent cutting-down
of capacity. It should be added that, where sufficient sand-free water
is being obtained without the attempt at gravel packing, the methods
that have proved successful should be followed. Where trouble is
encountered in getting water from fine-sand strata, it will be worth
while to experiment with gravel packing. It is highly important that
round, selected, washed material be used.
(3) A J in. pipe is now lowered into the well pipe to the bottom,
and a strong jet is pumped. This is done to clean the inside of
the well pipe and screen off any possible sediment, sand or dirt.
Finishing the Well
(1) The space between the well pipe and the earth hole should be
back-filled with compacted clay or concrete to prevent
contamination from reaching the water table through this
space.
(2) The well is now complete, and the hand-pump is installed
and operated continuously for (at least) eight hours per day
for three days to clean out the jetting water.
(3) A little hypochlorite of lime solution should be introduced
into the well, allowed to stand for 24 hours, and then pumped
out again.
(4) A watertight platform should be constructed to complete
the well.
55
APPENDIX G
Relative Merits of Pumps for use in Small Water-Supply Systems
(Reproduced from WHO Monograph Series No. 42)
VELOCITY
POSITIVE DISPLACEMENT
Types of
pumps
chain or
continuous
bucket
hand pumps,
plunger type
motor, wind
driven,
plunger type
Efficiency
range (%)
Low ; can be
improved
with double
acting
cylinders :
25%-60%
Low ; can be
improved
with double
acting
cylinders :
25%-60%
Low
good :
50%-85%
Operation
Very simple
Simple
Very simple
Maintenance
Simple, but
valves and
plunger
require
attention ;
more
difficult when
pump
cylinder is in
the well
Same as hand
pump ;
maintenance
of motors
sometimes
difficult in
rural areas
Simple
Ln
deep-well
turbine
jet
air-lift
good :
65%-80%
Low:
40%-60%
Low:
25%-60%
Simple
More
difficult;
needs
attention
Simple ;
air-locks can
cause trouble
More
difficult
compressor
needs
attention
Simple but
attention
necessary
More
difficult and
constant
skilled
attention is
necessary
Simple but
attention
is necessary
Compressor
needs
constant
attention
centrifugal
Capacity
gallons/
minute
2-10
9-22
3-15
Very wide
range : to
unlimited
Very wide
range ;
22-4,500
5-110
5-2,500
Head
(feet)
Low
High
Low
16-1,650
75-1,650
Low
Low
Cost
Low, but
higher when
cylinder is in
the well
Low, but
higher when
cylinder is in
the well
Reasonable
Reasonable
Higher
especially in
deep wells
Reasonable
Reasonable
Advantages
Low speed ;
easily
understood
by unskilled
people;
low cost
Low cost;
simple ; low
speed
Simple ; easy
to operate and
maintain
Efficient;
w’ide range
of capacity
and head
Good for
small diameter
bore-holes ;
ease of
operation
Moving parts
on surface ;
ease of
operation
Monng parts
on surface;
can pump
turbid and
sandy water
Dis
advantages
Low'
efficiency
limited use ;
maintenance
more
difficult
w’hen cylinder
is in the well
Low'
efficiency;
limited use ;
maintenance
more
difficult
w’hen cylinder
is in the well
Low
efficiency;
limited use
Moving
parts
and
packing
require
attention
Moving
parts in well:
rather
expensive ;
requires good
maintenance
and
operation
Limited
application;
low’
efficiency ;
moving parts
require
attention
Limited
application
low’
efficiency;
compressor
requires
constant
attention
Power
Hand or
animal
Wind, motor
Hand, animal
wind, motor
Motor
Motor
Motor
Motor
Ln
A -»
B «=■
C ■=
D =
E =>
F «=»
H «
Water level in well
Windlass
Guide hole for rope
Stop hook
Trough
Tight cover, removable
Compacted clay,
or concrete grout
A — Water level in well
B
Windlass
C — Guide hole for rope
D — Stop hook
E — Trough
F — Tight cover,
removable
G — Discharge opening
H — Compacted day, or
concrete grout
I — Weight attached to
top aide of bucket
to make it tilt when
bucket is lowered
onto water surface
Fig. No. 23 :—A sanitary rope and bucket well.
58
Water is elevated in small buckets at
tached to a belt which continuously carries
it to the surface. This is a fairly foolproof
system, with little maintenance required.
The original cost is considerable, but the
pump could be made locally from local
materials. Note the location of openings
(A) of buckets.
(Reproduced from WHO Monograph Series No. 42)
Fig. No. 24 :—A continuous belt bucket pump
A ~ Down-stroke: Cylinder above plunger fills while valve at base
of cylinder closes, and valve in plunger opens.
B —Upstroke: Cylinder full of water above plunger is expelled
while, at the same time, valve at base of pump opens, filling
cylinder below plunger. As plunger rises, a vacuum is formed
below, pulling water into the cylinder.
When the cylinder is above ground, a foot valve is necessary to
avoid pumping.
Fig. No. 25 :—A hand-operated Displacement Pump.
59
A self-priming lift-and-forcc pump which can
be fitted to deliver water from wells to ground
level, or to an overhead tank.
(By kind permission of Lee, Howl & Co. Ltd., Tipton, Staffs.)
Fig. No. 26
Another type of self-priming
lift-and-force pump which may be
driven by hand or by power.
Suitable for use in villages and
rural supplies.
(By kind permission of Lee, Howl & Co. Ltd.,
Tipton, Staffs.)
Fig. No. 27
60
SUPPLIERS OF WATER EQUIPMENT
The Permutit Co. Ltd.,
Pemberton House, 632/652 London Road, Isleworth, Middlesex.
Paterson Candy International Ltd.,
21 The Mall, Ealing, London, W.5.
United Filters & Engineering Ltd.,
25 Raleigh Gardens, London Road, Mitcham CR4 3UP, Surrey.
Bell Bros. (Manchester) Ltd.,
Ashton Road, Denton, Manchester M34 3LS.
William Bony & Co. Ltd.
23 High Street, Rickmansworth, Herts. WD3 1HP.
C. M. Wales Ltd.,
Piltdown Lodge, Piltdown, Uckfield, Sussex.
61
PUBLICATIONS OF THE ROSS INSTITUTE
The Preservation of Personal Health in Warm Climates.
(7th Edition, March, 1971; Revised and Reprinted, July 1974)
(A handbook for those going to the tropics for the first time)
Ross Institute Bulletins:—
(1)
Insecticides. (Reprinted) October, 1973.
(2)
Anti-Malarial Drugs. (Revised) April, 1975.
(3)
(Out of Print.)
(4)
Tropical Ulcer. (Revised) August, 1973.
(5)
The Housefly and its Control. (Reprinted) July, 1973.
(6)
Schistosomiasis. (Reprinted) May, 1974.
(7)
Malaria and its Control. (Reprinted) May, 1974.
(8)
Rural Sanitation in the Tropics. (Reprinted) May, 1974.
(9)
The Inflammatory Diseases of the Bowel. (Revised)
August, 1970.
(10)
Small Water Supplies. (Reprinted) April, 1975.
(11)
Anaemia in the Tropics. (Reprinted) June, 1974.
(12)
Protein Calorie Malnutrition in Children. (Reprinted)
June, 1974.
These publications are revised from time to time and new and revised
editions are issued as occasion warrants. They are available at printing
cost plus postage on application to:—
The Publications Secretary,
The Ross Institute,
London School of Hygiene & Tropical Medicine,
Keppel Street (Gower Street),
London, WC1E 7HT
Tel: 01-636 8636.
62
Position: 1301 (4 views)