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Un] MICROFICHE
REFERENCE
jqh LIBRARY
A project of Volunteers in Asia
Purification of Water on a Snail -^J^
Technical Paper he. 3
Published by;
International Reference Centre for Community
Water Supply
P.O. Box 5500
2280 HM Rijswijk
The Netherlands
Available from:
International Reference Centre for Community
Water Supply
P.O. Box 5500
2280 HM Rijswijk
The Netherlands
Reproduced by permission of the International
Reference Centre for Community Water Supply.
Reproduction of this microfiche document in any
form is subject to the same restrictions as those
of the original document.
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WORLD HEALTH ORGANIZATION
INTERNATIONAL REFERENCE CENTRE FOR COMMUNITY WATER SUPPLY
TECHNICAL PAPER NO. 3
The Purification of Water on a Small Scale
MARCH 1973
THE HAGUE — THE NETHERLANDS
- 3 -
Introduction
In 1956 Mr. R.N. Clark of The Division of Environmental Sanitation of
the World Health Organisation in Geneva prepared a note on the Purifica-
tion of Water on a small scale which was published in the Bull. Wld. Hlth.
Org. 1956, 2!t' 820-826.
There is a great need for these practical instructions, especially for
rural areas, where health conditions leave much to be desired and no
sanitary drinking water supply exists.
In connection he^ with W.H.O. suggested to the I.R.C. for Community Water
Supply to repub sh this paper, including new data available.
This I.R.C. technical paper no. 3 resulted from collaborative efforts
between I.R.C. and W.H~0 o and it is intended to be used by the latter
organisation in its briefing of new consultants. It is hoped that the
paper will be of use to them and also to many others working in the field
of water supply.
I.R.C. will highly appreciate receiving any contribution, which may further
improve this paper..
- 5 -
THE PURIFICATION OF WATER ON A SMALL SCALE
There are three general methods for the purification of water on an indi-
vidual or domestic scale:
1. Boiling
2. Chemical disinfection, and
3- Filtration
These methods can be used singly or in combination.
1 . Boiling
Boiling is a satisfactory ""-^thod for destroying disease organisms in water
and it is equally effective whether the water is clear or cloudy, whether
it is relatively pure or highly contaminated with organic matter. Boiling
destroys all forms of disease organisms usually encountered in water,
whether they be bacteria, spores, cercariae, cysts or ova.
The amount of fuel required to boil water varies with the type of fire,
stove, and vessel. Under the conditions usually associated with the boil-
ing of drinking water, it requires about 1 kp- of wood to boil one litre
(approx. 2 lb per quart).
To be safe, water must be brought to a f, r< ^il". The appearance of
bubbles (simmering) is sometimes confused ^oiling, as is the appear-
ance of mist or steam over the water. None oi .„X.-se signs is sufficient
indication that water has reached a boiling temperature. Having reached
boiling point the water should continue to boil for at least five minutes.
Five minutes will be the minimum suitable to low level locations, say,
below 1000 metre elevation and, as a rule, one minute ftirther boiling
should be given for locations at intervals of height above sea-level of
1000 metres, the reason being that water will boil at lower temperatures
at higher altitudes.
It is also recommendeu that turbid or cloudy water be boiled somewhat
longer than clear water. It is good practice to boil water in the same
container in which it is to be cooled and stored and to use this contain-
er for no other purpose.
HOLE 1CM DIA
ifi
1 KG BLEACH-
ING POWDER'
•2 KG SAND •
FIG. 1 CHLORINATION POT FOR HOUSEHOLD WELLS
CAR 400 LITRES PER DAYdOOGPD) OF DRINKING WATER
CHEMICAL RECHARGE EVERY 3 WEEKS
(SOURCE: C P HE Rl . NAGPUR, INDIA)
36648
- 7 -
Boiling alters the tase of water because it drives out dissolved gases,
particularly carbon dioxide. The practice of aerating water by stirring
or by pouring from one container to another is not recommended as this
makes for a serious risk of recontamination . Water left for a period of
several hours, up to a day, in a partially filled container, where there
is a good air surface exposed, even though the mouth of the container is
covered, will lose most of the boiled taste in particular if stored in
a refrigerator. In any case, it is preferable to be reconciled to the
inoffensive taste of boiled water than to run the risk of drinking pol-
luted water
2. Chemical disinfection
Where a house has its own private well as its source of drinking water,
the water can be disinfected in the well. Research into simple but
ef ;: ient methods of disinfection has resulted in several successful
designs using chlorine. Fig. 1 . illustrates a double jar chlorinator
developed at the Central Public Health Engineering Research Institute,
Nagpur, India. An alternative method of disinfection by means of iodine
is still in development with the W.H.O. International Reference Centre
for Community Water Supply.
For water brought into the house from outside sources, simple chemical
treatment can be given to ensure its safety. The two chemicals recommen-
ded on the grounds of efficiency and easy availability are chlorine and
iodine .
Chlorine
Chlorine is a useful disinfectant for drinking water and is effective
against the bacteria commonly associated with water-borne diseases. In
the usual doses, it is not effective against certain cysts and ova,
nor against organisms embedded _n solid particles. Chlorine enters al-
most instantaneously into chemical combination with organic matter in
water and in such "combined" form, is only of limited use for disinfection.
Sufficient chlorine must therefore be added to satisfy tiie "chlorine de-
mand" of water in addition to the amount required for bacterial action.
- 8 -
This combination with other substances may give rise to a chlorine taste,
but the presence of such a taste gives some indication that a "free
chlorine" residual exists. In general, a cloudy water, or highly pol-
luted water, containing large quantities of organic matter, is not
suitable for chlorixiation . Turbid water can be filtered, and when clear,
it can be successfully chlorinated.
Experience indicates that a contact period of about 20-30 minutes is
necessary for the chlorine to destroy harmful bacteria.
Chlorine is easiest to apply in the form of a solution. A good stock
solution to use in treating water contains about 1% available chlorine.
This is about the strength of proprietary disinfectants such as "Milton",
"Zonite" or "Javel water".
Other easily available sources of chlorine are the commercial laundry
bleaches sold under a variety of trade names (see Annex 1) . These will
usually contain about 3% to 5% available chlorine and can be easily
diluted to a 1% solution by addition of appropriate quantities of pure
water .
It is also possible to purchase bleaching powder or chlorinated lime.
This is a white powder which contains about 30/6 available chlorine when
freshly made. However, the strength of this powder rapidly diminishes
after the container is opened. Storage over a long period, even without
opening, can also result in a loss of strength. In using chlorinated
lime, it is best to use the whole container at once, immediately after
opening, to make up a stock solution. The inert lime will settle in a
few hours leaving the active chlorine in the clear solution which can
then be poured off and kept In a tightly stoppered bottle for future use.
This stock solution is still subject to chemical degradation which com-
plicates the reliability of dosing.
Another type of powder is high-test hypochlorite, which contains about
70% available chlorine. Containers of this powder should be kept as cool
as possible, there having been instances of cans bursting when left ir.
the hot sun or in hot storage places. The powder can be used to make a
stock solution in the same way as chlorinated lime. High-test hypochlor-
ite is more stable than chlorinated lime, and will keep its strength
better after the container is opened, so it is not necessary to use the
whole container at once. However, even this material will lose most of
its strength in a month or two after the container is opened.
Chlorine solutions are unstable in warm climates. They phould be kept
in brov/n or grc^en bottles, well stoppered and stored in dark, cool.,
places .
To make a litre, (one ... , t) of about VX st<- •': . -lution, add the re-
quisite amount of rat-r to any of the following:
oither 250 nil (1 cup) of liou. J laundry bleach,
or ^+0 g (2| tablespoons) of cnlorinated lime,
or 15 g (1 tablespoon) of high-test hypochlorite.
Smaj-ler-- quantities of stock solution can be made by using proportionate
amounts.,.
The proprietary dit;: :\i 'a - tants , o: which ex? tples have be . .1 given, general-
ly have a 1% solution strengtn and can be uf.--.ed without dilution.
To chlorinate water, add three drops of 1% solution to each litre (quart)
of water or one fluid ounce to 32 imperial gallons. If the water is
clear but highly coloured, like very weak tea, or if it has a noticeable
sulphur odour, the dosage should be doubled. It is repeated that a con-
tact period of about 30 minutes should be allowed before use to ensure
complete disinfection.
Chlorine is also available in tablet form, of which the following are
examples of commercial brands which may be available: "Halazone" and
"Chlor-deshlor"; other brand names are given in Annex 1. Directions for
use as given on the package should be followed carefully. For example,
Chlor-dechlor has a double action. This tablet first disinfects the water
with a special chlorine compound. Then, after the outer portion of the
tablet dissolves, the inner core neutralizes the remaining chlorine to
reduce the taste. If more than one tablet is to be used, the whole
amount must be put in at the same time. Tablets added after the dechlor-
inating core of even one of these tablets is dissolved are completely
ineffective.
The foregoing practices are all related to water within the house. Fig. 1.
illustrates a practice suitable for well chlorination .
Iodine
Iodine is an excellent disinfecting agent and, as tincture of iodine, is
normally available from any chemist. In addition, water disinfectants
abased on iodine are commercially available, an example of which is "Glo-
baline". Each tablet contains sufficient iodine to disinfect one litre
(one quart) of clear water by liberating 8 mg of iodine; for turbid or
- 10 -
highly polluted water, two tablets are recommended. Contact period
prior to use should be not less than 20 minutes and in very cold cli-
mates this should be increased to 25 minutes. Other makes are shown
in Annex 1 .
If tincture of iodine is used to disinfect water, normally two drops
of 2% strength will suffice for one litre of water. However, water
which is cloudy or muddy, or water having noticeable colour, even when
clear, is not well suited for disinfection with iodine solution.
Turbid water can be filtered and the clear filtrate can then be treated.
If the water is known or suspected to be heavily polluted, the dose
should be doubled. There is no harm in using the higher dosage, but it
will produce a medicinal taste.
The commercially produced tablets are normally iodine compounds, such as
tetraglycine potassium tri-iodine, and are effective against amoebic
cysts, cercariae, leptospira, and some viruses as well.
When iodine is the disinfectant a similar contact period to that recom-
mended for chlorine should be followed, i.e. 20-30 minutes. When using
proprietary tablets the manufacturer's instructions should be carefully
read and followed.
Potassium Permanganate
Potassium permanganate has frequently been used for the disinfection of p ;
water. It is a powerful oxidizing agent, on which account its action is
rapidly spent in waters containing organic material. The commonly used
dosage is one part in 2000 or 0.5 g/1. Potassium permanganate may possibly
be effective against the cholera vibrio, but it is of little use against
other disease organisms. Water treated with potassium permanganate in
time produces a dark brown precipitate, which is difficult to remove
without scouring. The opinion is expressed that potassium permanganate
is not a satisfactory disinfectant and its use is not recommended.
- 11 -
3. Filtration
There are two types of filters commonly used for the treatment of house-
hold water supplies: the sand filter, which is relatively coarse; and
the ceramic filter, which is of a finer texture. There is also the
carbon filter ( Fig. 2. ) the prime purpose of which is removal of excess
chlorine.
Sand filter
The household sand filter, unless skillfully operated, is relatively in-
effective against bacteria. It will, however, remove cysts, ova, cer-
cariae, and similarly large organisms, -and will strain out most of the
coarse and visible matter in suspension, although it may pass some fine
turbidity or cloudiness. Sand filtration may be made more effective by
first carefully treating the water with alum, as a result of which a
clear water can be obtained. Some household filters contain charcoal.
This has almost no purifying effect, its function being to absorb certain
taste-producing compounds, but even this effect is lost unless the char-
coal is frequently renewed. Charcoal filters have the property to absorb
organic matter, which can serve as nutrients causing an undesirable bac-
terial growth in the filter. There are instances of filtered water having
a higher bacterial count than the unfiltered water. To a lesser extent
this can also happen with sandf liters. From a hygienic point of view
these filters should not be used as a single step of treatment. Subse-
quent to filtration the water should be boiled or disinfected.
With this reservation in mind, the household sand filter finds a definite
place in water treatment. It can easily be made for household use where-
ever fine sand is found. The essential points in making a filter are,
firstly, that the depth of sand through which water passes should be at
least 60 cm (2 ft) - an additional 15 cm (6 inch) is, in fact, desirable -
and, secondly, that the rate of flow through the filter should not be
greater than 200 x/m 2 /hr (k Imp. gall./ft 2 /hr or ^.8 US gall ./f t 2 /hr ) .
A simple filter can be constructed from a steel drum 60 cm (2k inch) in
diameter and 75 cm (30 inch) high, with the head cut off. Place the drum
on a stand, with a container underneath, and drill a hole 2 mm (3/32 inch)
in diameter at the bottom of the drum to serve as the filter outlet.
I.R.C.
THE NETHERLANDS
1972
24 INCHES INLET
FIG. 3 SAND FILTER
CAPACITY 1 LITRE / MIN (12 GPH)
Place a few centimetres of small stones, about pea-size, in the bottom
of the drum and fill to within 10 cm (4 inch) of the top with rather
fine sand. Make a hole in the side of the drum just below the top rim
for an overflow and insert a short length of pipe for an overflow line.
A general layout of such a filter is illustrated in Fig. 3 . Drums initial-
ly used for oil or chemicals should not normally be used as they may be
heavily contaminated. The drum used should be thoroughly cleaned out and
disinfected prior to use.
The sand and stones are also likely to be contaminated -And have to be care-
fully cleaned before the filter is assembled. The filter should then be
filled with highly chlorinated water and allowed to stand for 2 hours before
draining to waste.
To operate the filter keep a continuous flow of water running into the
top, just sufficient to keep the filter filled, with a slight overflow.
It may be necessary to place a small disc on the surface of the sand under
the inlet to prevent a hollow forming in the sand. A filter of these di-
mensions should deliver one litre per minute (12 gallons per hour) of
clear water, which should nevertheless be chlorinated prior to drinking.
In operating such a filter, it is desirable to keep a continuous flow
through the filter at all times. The rate of filtration is likely to
fall off in time, but the filter should be cleaned only at long inter-
vals possibly of several weeks or even months, since its efficiency de-
pends highly on the biological growth on the surface of the sand. A slow
sand filter as described, is a reliable barrier to disease organisms,
(even when the after chlorination is failing because of chemical degre-
dation of the chlorine solution).
Passage of organisms, however, will occur in the first week after the
start of a newly constructed filter and after cleaning of the filter as
described below. Trouble with green growths (algae) can be eliminated
by covering the filter to keep it perfectly dark, since this green algae
depends on light for growth. When it becomes necessary to clean the
filter, a very thin layer, about \ cm (1/4 inch) can be carefully scraped
off and discarded, following which the sand surface should be lightly
raked or scratched to leave it loose. After several such cleanings, the
sand should be restored to its initial level with clean sand after
scraping the filter surface down to a clean level.
I.R.C,
THE NETHERLANDS
1972
PLASTIC TUBE
t DRINKING WATER
FIG. 2 CARBON FILTER
FOR REMOVING EXCESS CHLORINE
(SOURCE: MIN. OF HEALTH, INDONESIA)
36649
- 15 -
For more turbid waters, settling or coagulating and settling prior to
filtration may be necessary. The latter may be carried out in a .. ^ f araie
steel drum by stirring a solution of one tablespoon ( 10 g) of aliai into
100 litres of the water to be treated for about three minute- until a
floe starts to form, followed by adding 10 g (one tablespoon) of cal-
cium carbonate under continuous stirring. A period of about half an
hour should be allowed for the floe to settle; the settled water is then
ready for filtering.
Ceramic filters
There are several types of ceramic filters, such as pressure filters,
non-pressure filters, and filter pumps, and there is a wide range of
ceramic media uaving different pore sizes. The heart of any of these
is the filter candle, and the method of getting water through the candle
is only a matter of convenience. Only clean water should be used with
ceramic filters, otherwise, with cloudy or turbid water, the candles clog
very quickly.
Coarse-grained filter candles are useful in removing suspended matter,
helminth ova, cercariae, and cysts. They may only partially be effective
in removing the smaller disease organisms, and consequently water should
always be chlorinated or otherwise disinfected after passage through a
coarse-grained or industrial-type filter.
Porcelain filters are made with pore sizes from a radius of 50 u or
larger down to 0.30 |i . To be satisfactory for water purification, the
maximum pore radius should be about 1.5 U • Examples of such filters are
the Chamberland and the Selas 015- These and similar fine-grained
porcelain filters will remove all disease organisms usually found in drin-
king water during a limited period of time, and it is quite safe to use
water after passage through such a filter without further treatment.
After a prolonged use, however, the bacterial growth will penetrate and
pass the filter. This breakthrough can generally be prevented by cleaning
and boiling the filter at least once a week, even if the filter does not
clog. If a filter gets coated or clogged, it should be scrubbed under-
running water with a stiff brush free from soap, grease, or oil, and then
boiled for 15 or 20 minutes.
- 16 -
Another type of filter candle is known as the Kieselguhr, or infusorial
or diatornaceous earth filter. Like the porcelain, this also is made with
various pore sizes. The finer-grained types are efficient in removing
all types of bacteria commonly found in water. Among the well-known
Kieselguhr filters are the Berkefeld and Mandler filters. Their poro-
sity is graded as V ("viel", or course), N (normal, or intermediate),
and W ("wenig", or fine). The V filters are suitable only for the re-
moval of suspended material, and following filtration with this type of
candle, the water should be further treated to destroy bacteria. The
N filters remove the smallest bacteria, and it is safe to use water fil-
tered through this grade without further treatment. The same care should
be taken of Kieselguhr candles as of porcelain candles, except that they
should be cleaned more frequently, at intervals of not longer than four
or five days at the most.
There is a special type of filter candle, known as the "Katadyn" filter,
in which the surface of the filter wall is impregnated with a silver
catalyst in such a way that the porosity is not impaired, but the bac-
teria coming in contact with the surface are killed by oligodynamic
action. Such a filter needs cleaning only when it becomes clogged. /
Above filters and their attachments should be carefully examined at
frequent intervals to guard against cracks or leaks which might possibly
permit unfiltered water to get by. For this reason and from a hygienic
point of view, the filtered water should also be disinfected with chlorine.
Filter candles can be mounted in a gravity-type filter, which consists
of two reservoirs with the candle or candles attached to the upper one.
Water is simply poured in at the top, trickles through the ceramic candles,
and is stored for use in the lower compartment. Another mounting is made
where piped water is available under pressure. The candle is mounted in
a pressure case which is attached directly to the water system, filtered
water being drawn from the filter as needed. A third type is fitted with
a hand pump. The suction tube is put into a vessel of water, and the
pump is operated like a bicycle pump, the filter candle being inside.
The filtered water is discharged through another tube. Any of these
systems is satisfactory if suitable filter candles are selected.
Water storage
No matter how much care is taken in producing safe water, this will be
nullified if the water is contaminated after treatment. If boiled or
filtered water is "unprotected" it may be subjected to immediate re-
contamination. Water treated with chlorine or iodine has "residual
protection" which will successfully deal with light recontamination for
a considerable period of time. However, this residual effect eventual-
ly disappears unless additions of chemicals are made. It is very impor-
tant to keep the treated water free from the hazards of recontamination.
The principles are simple. Use clean vessels to store water; do not
dip anything into the water; and keep the vessels covered to prevent
the entry of insects, dust, or other foreign substances.
Cleanliness of the storage vessels involves periodic emptying, --'ashing,
and rinsing with heavily chlorinated water, to prevent the accumulation
of slime growths.
Wherever practicable, small-mouthed vessels should be used with a neck
narrow enough to prevent the entry of a dipper, cup or hand. When large
vessels are used, arrangements should be made for easy pouring, either
by tipping or by rolling the vessel. The best scheme with large vessels
is to use, if possible, a spigot.
To prevent the entry of dirt, dust and other foreign matter, some form
of cover is necessary, preferably of impervious washable material. The
form and type of cover depends primarily on the vessel. It should be
tight enough to keep out flies, wasps, roaches, and other insects, and
substantial enough not to be easily lost or broken.
Another precaution relates to the use of commercially produced bottled
water and carbonated beverages. The fact that such products are put
into bottles and capped does not ensure their purity. When water is
bottled, its bacterial content decreases with time, but cysts and ova
may survive long periods of storage. The amount of sugar in sweetened
drinks determines their bactericidal properties, but complete safety de-
pends on initial purity and long storage.
In the case of carbonated beverages, the carbon dioxide does inhibit
bacteria, hut its action is selective, since some organisms are more
resistant than others. Carbonation alone cannot be counted on to make
a beverage safe. Thebest policy would seem to be to use only beverages
- 18 -
bottled in establishments reliably known to use pure ingredients and which
maintain a suitably high standard of plant hygiene and standards of
operation.
It is also relevant to mention that ice, too, can harbour contamination.
Ice cubes should be made from properly treated water; that means, from
chlorinated drinking water or piped water from a public water supply.
Unless the ice is reliably known to be pure, it should never be put
directly into the beverage itself, but only packed round the beverage
containers to effect cooling.
Conclusion
In conclusion, when dealing with drinking water it is safest not to take
anything for granted. It is frequently, and often wrongly, assumed that
all large cities have safe water supplies. Unless the validity of this
assumption is established, it would be safer to leave nothing to chance.
The transient traveller in particular, would be well advised to do his
own unobtrusive job of water purification.
Summary of treatment
Type of water.
Recommended processes for rendering
water suitable for drinking.
1 .
All types
boiling
2.
Clear water
chlorination (disinfection)
3-
Slightly turbid
filtration and disinfection
k.
Turbid
settling, coagulation, filtration
and disinfection
5.
Special types, e.g.
excessive hardness,
corrosive, high
content o: minerals
such as iron or
seek professional advice for
special treatment
manganese
- 19 -
ANNEX 1 .
PROPRIETARY NAMES OF SOLUTIONS OR TABLETS SUITABLE FOR WATER PURIFICATION
FOR INDIVIDUAL USAGE.
The following proprietary names are given for information- only-* ■ The -
mention of specific companies or of certain manufacturers' products does
not imply that they are endorsed or recommended by WHO or the WHO Inter-
i
national Reference Centre, in preference to others of a similar nature
which are not mentioned.
1 . Sources of chlorine
a. Solid form
"Halazone" - tablets (Use as directed
"Chlor-dechlor" - tablets C " " "
"Hydro-chlorazone" - tablets ( if " "
"Halamid" - tablets ( M " "
"Chloramin-T Heyden" - tablets ( " " "
b. Liquid form
"Zonite" - liquid (approx. 1% chlorine solution - can be
used as supplied)
"Milton antiseptic" - liquidC " " " " )
"Javel water" - liquid ( " " " " )
"Dankin's solution" - liquid(approx. 0.5% chlorine solution)
and other commercial
laundry bleaches, e.g. (usually 3-5% chlorine solution - dilute
"Clorox", "Dazzle" and t0 V ^
"Regina"
2. Sources of iodine
a. Solid_f orm
"Individual Water Purification Tablets" - tablets (use as directed)
"Portable Aqua" - tablets ( " " " )
"Globaline" - tablets ( " " " >
B. Liquid form
"Lugol's solution" - liquid (approx. 5% iodine solution)
"Tincture of iodine" - liquid (approx. 2% iodine solution)