There are a number of water treatment measures that can be adopted such as: storing water, boiling water, pasteurisatiion, filtration and chlorine. Thou these methods each have their limitations; either they are costly or do not completely cleanse the water.

There's a simple cost effective solution that can be adopted providing the sun is shining.

The Solution
SODIS (Solar Water Disinfection) - a simple, low-cost and easily replicable solution to clean drinking water. SODIS works through a combination of heat and pathogen-killing Ultra Violet radiation (both through sunlight).

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. Check if the screw cap is water tight and clean.
4. Fill bottles with water. 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.
5. Lay bottles out on a suitable heat-reflecting surface – roofing sheets, CGI (Corrugated Iron) sheets etc, in a clear spot on the roof or garden.
6. Expose bottles to direct sunlight for at least six hours.
7. After 6 hours water is clean and safe to drink.

How successful is SODIS?
SODIS is 99.9% effective against pathogenic micro-organisms found in water. This may not be as good as boiling which provides pathogen-free sterile water or even pasteurisation. But, in terms of cost, affordability, simplicity and sustainability, SODIS scores over these other methods.

SODIS reduces the incidence of infectious diarrhoea, dysentery, and also protects against cholera.

Which micro-organisms is SODIS effective against?
The sun’s radiation is proven to be deadly to human pathogens, which are used to living in the moist, humid, dark environment inside the body. Once they are discharged into the wider environment, these pathogens are extremely sensitive to conditions outside. UV radiation can be fatal to many such pathogens, while others are inactivated by maintaining a 50-57 ̊C heat in the bottle for a given period of time.