Household Water Treatment and Safe Storage Factsheet: Source ...

Household Water Treatment and Safe Storage
Factsheet: Solar Disinfection (SODIS)
UV radiation is reduced at increasing water
depth. Bottles used for SODIS should not
exceed 10 cm in water depth, such as 1-2
litre volume PET bottles placed on their
sides in the sunlight (EAWAG/SANDEC,
2002).
Heavily scratched and old bottles should be
replaced since they reduce the amount of
UV light that can pass through (Wegelin et
al. 2000).
The source water should first be sedimented
and/or filtered if turbidity levels are greater
than 30 NTU, (Sommer et al, 1997).
Fill the plastic bottle ¾ full of low turbidity
water. Shake the bottle for about 20
seconds and then fill the bottle completely.
Place the bottles horizontally on a roof or
rack in the sun for the following times:
6 hours if the sky is cloudless or up to
50% cloudy
2 consecutive days if the sky is more
than 50% cloudy
Do not use SODIS during days of
continuous rainfall.
The efficiency of SODIS is dependent on the
amount of sunlight available. The bottles
must NOT be placed so that they are in
shade for part of the day. The most
favourable geographical regions for SODIS
are located between latitudes 15 o N and
35 o N (as well as 15 o S and 35 o S). The
majority of developing countries are located
between latitudes 35 o N and 35 o S
(EAWAG/SANDEC, 2002).
The treatment efficiency can be improved if
the plastic bottles are placed on sunlight
reflecting surfaces, such as corrugated
aluminum or zinc roofs. This can increase
the water temperature by about 5°C. This
has been found to be especially beneficial in
low sunlight conditions when the disinfection
process is the slowest (Mani et al., 2006).
The treated water should preferably be used
directly from the bottle to minimize the
possibility of recontamination. Nonpathogenic
organisms, such as algae, may
grow in the conditions created in a SODIS
bottle (EAWAG/SANDEC, 2002).
(Credit: EAWAG/SANDEC)