SODIS (Solar Water Disinfection) is an initiative of Eawag, the Swiss Federal Institute of Aquatic Sciences and Technology.
The aim of the scheme is to reduce the infant mortality rate by helping to provide people in developing countries with access to clean drinking water.
SODIS uses a simple technique to ensure water is clean enough to drink.
Clear Polyethylene Terephthalate (PET) bottles are filled with the water and set out in the sun for 6 hours. The UV-A rays in sunlight kill germs such as viruses, bacteria and parasites.
The slideshow below shows the process of the sunlight killing the germs in the bottle.
Two clear PET bottles
This is relatively cheap as it uses recycled materials. It is appropriate for developing countries due to typical hot temperatures and sunny climates.