SODIS
Practical Action
Research on SODIS has shown that these pathogens are destroyed during the process.
Bacteria - Escherichia coly (E.coli), Vibrio cholerae, Streptococcus faecalis, Pseudomonas
aerugenosa, Shigella flexineri, Salmonella typhii, Salmonella enteritidis, Salmonella paratyphi
Virus - Bacteriophage f2, Rotavirus, encephalomyocarditis virus
Yeast and Mould - Aspergillus niger, Aspergillus flavius, Candida, Geotrichum.
The effect of SODIS on cyst forming protozoa like Entamoeba hystolitica, Giardia intestinalis,
Cryptosporidium parvum and helminthes has not been systematically assessed. But, studies
show that these have a thermal death point of around 57ºC. If the water maintains a
temperature of 57ºC for a minute or a 50ºC temperature for one hour, many cyst-forming
types will also be eliminated.
How to do it?
1. Check if the climate and weather conditions are suited for SODIS – basically there should
be fairly bright weather with not more than 50% cloud cover.
2. Collect plastic PET (Poly Ethylene Terephthalate) bottles of one litre or 1-1/2 litre
volume. PET is preferred to PVC, because PVC can contain harmful additives and to
glass, because glass blocks out some of the UV rays.
3. Each family member should be assigned two bottles per day. So a family should have
four plastic bottles per member – two for the day’s consumption and two exposed to the
sun.
4. Check if the screw cap is water tight and clean.
5. Bottles should be laid out on a suitable heat-reflecting surface – roofing sheets, CGI
(Corrugated Iron) sheets etc, in a clear spot on the roof or garden. The bottles should be
exposed to direct sunlight for at least six hours.
6. Check if the water is clear enough. If there is a lot of discolouration and sediment, the
water has to be pre-treated (filtered) before SODIS.
7. It is best to have a specific person responsible for
exposing the SODIS bottles to the sun, and at least
two members of each family must be trained in the
correct application of SODIS, especially on the
importance of maintaining sun exposure throughout
the period.
How to increase the efficiency of SODIS?
There are certain practices that can increase the efficiency
of SODIS. These have to do with increasing sunlight
exposure, harnessing available sunlight better and
quickening the heating-up process for SODIS water.
Putting black paint on half of the outer surface of
the PET bottle and laying the bottle blackened-
side downwards increases the rate of heating.
Placing the bottles on a reflective surface-
aluminium foil etc – can dramatically increase the
water heating rate.
5
Figure 3: The back face of the
bottle can be painted black to
help absorb solar energy thus
heating the water. Photo: Practical
Action / Zul.