The SODIS method of water purification is simple and inexpensive. It utilizes the UV rays from the sun and temperature to kill harmful bacteria and parasites. The steps are listed below.
NOTE: If the water is cloudy, it MUST be filtered first in order for this method to be effective.
A simple filtration method is to first filter the water through a container filled with sand. If there are a lot of particles floating in the water it will help to first filter it through a container filled with small gravel and then through a contain filled with the sand. Small holes should be punched in the bottom of the containers so that there is a slow filtration rate.
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For detailed information, see http://www.sodis.ch/index_EN
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PET bottles are recommended in the application of the SODIS method because they are light and do not break. They are also easy to obtain in many regions. However, glass bottles or special bags can also be used. PET or PETE bottles are usually labeled as such, but they are not called by the same name in all countries. The bottles must be transparent and colorless. PET bottles often have a bluish tinge. This is not a problem. Heavily scratched bottles must be replaced.
If the water is very turbid, the effectiveness of the method is reduced. It is very easy to determine whether the water is sufficiently clear:
The filled PET bottle must be placed on top of a newspaper headline. Now one must look at the bottom of the bottle from the neck at the top and through the water. If the letters of the headline are readable, the water can be used. If not, the water must first be filtered.
Cloudiness affects the strength of solar radiation and thus also the effectiveness of the method.
Rule of thumb:
- If less than half of the sky is clouded over, 6 hours will be enough to completely disinfect the water.
- If more than half of the sky is covered with clouds, the bottle must be placed in the sun for 2 consecutive days.
The method does not work satisfactorily during lengthy periods of rain. On these days, we recommend collecting rainwater.
The treated water should be kept in the bottle and drunk directly from the bottle, or poured into a cup or glass immediately before it is drunk. In this way, it is possible to prevent the treated water from becoming contaminated again.