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The following instructions are intended primarily for the benefit of
housewives in rural areas in developing countries where safe community
water supplies are not available. It is assumed that in these areas
water-borne diseases are endemic or sporadic.
These instructions concern the procedure to be adopted on a routine
basis for the proper disinfection of drinking water for household use.
The procedure involves exposure to sunlight of water from the usual
community source for a minimum period of time in available transparent
containers such as colorless or blue-tinted glass or plastic bottles.
In order to save time and effort, it is highly desirable for a
housewife to make her own arrangements to carry out the routine
disinfection operation regularly once a day, or once every other day.
For this reason, a housewife should ensure enough containers that would
hold the desired quantity of drinking water estimated by her to meet the
needs of the family for one or two days.
At the end of the sunlight exposure period, a housewife could then
transfer indoors the whole set of containers for use. To avoid
recontamination, the already disinfected water should preferably be kept
in the same containers used in the solar exposure operation. However, if
there is a shortage of small containers, then the disinfected water
could be transferred from each exposed container to a clean large
container reserved for bulk storage of processed water.
Once a set of emptied containers becomes available after usage, the
refilling and exposure procedures are repeated. If the containers are
maintained in a good state of cleanliness, then there would be no reason
for having to clean them repeatedly each time they are to be re-used.
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1. Containers:
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 | From among those found at home, or purchased from the local
market, select a number of containers made of colorless or
blue-tinted glass or transparent plastic estimated to hold an amount
of drinking water sufficient for household consumption for one or
two days. The selected containers could include ordinary bottles,
jars, or any other types of vessels provided they are transparent to
light. Colored containers other than blue, or greenish-blue should
not be used as they are not as satisfactory.
| Remove any detachable paper labels from bottles, and wash all the
containers with water (and soap, if necessary) to remove dirt and
any residue from the previous contents. |
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2. Water:
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| Fetch water in the usual manner from the common village supply
(stream, well, pond, reservoir, etc.). If the water is highly
turbid, then clarify the water by allowing the suspended particles
to settle. Decant the clear water into other vessels.
| Carefully fill each of the containers hereafter reserved for the
solar disinfection operation with the clarified water. |
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3. Exposure:
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| Place the containers outdoors in an open space where sunlight
cannot be obstructed by houses, walls, trees, or bushes throughout
the day. Porches, balconies, roofs, or window sills would be
satisfactory if open land is not available. Select places away from
dust, children, domestic animals, and pets to avoid contamination
and mischief. Individual containers should be spread out to avoid
shadows.
| Keep the containers in their normal upright position. Tilting them
at an angle towards the sun (as is commonly advocated for other
solar appliances) may diminish the disinfection efficiency. Stoppers
for bottles, and original covers for jars may be used to prevent the
entry of dust, dirt, or vermin. But, such closures are not essential
for the disinfection process. In fact, water exposed to bright
sunlight in tightly closed containers could become much warmer than
that in open containers. This is because the water vapor escaping
from open containers carries with it some of the heat acquired by
the water exposed to sunlight.
| Since it is futile to maintain an exact time for sunlight
exposure, it would be a wise arrangement on a routine basis to start
the sunlight exposure operation at a convenient time in the morning,
and to keep the containers exposed until the late afternoon. The
exposed containers may then be kept in place overnight to allow the
water to cool, or they may be transferred indoors in readiness for
use. However, in such emergencies as when a family runs short of
disinfected drinking water, an exposure period of about two hours,
especially at noontime, should be adequate for proper disinfection.
These practical suggestions will ensure satisfactory results even
under moderately cloudy conditions. It would not be practical to
carry out the operation under conditions of heavy rainfall.
| After use, the empty containers can be re-used without the need
for rewashing unless they accidentally become dirty. The cycle can
now be repeated from the stage of refilling with water through the
stage of sunlight exposure. With time and experience, the whole
operation becomes a matter of routine. It should be noted that these
instructions need to be modified or simplified further by health
educators and primary health care promoters to suit local
conditions, provided the essential requirements are not altered in
any way. |
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