Sunshine on a Cloudy Day: Disinfecting Water around the World

SODIS allows people to disinfect their water using only a water bottle and natural sunlight. First, a clear (or blue-tinted) PET water bottle is cleaned with soap. Then, the bottle is filled with water and placed in full sunlight for at least six hours. The method kills bacteria and protozoan parasites and inactivates many viruses, significantly reducing the number of children falling victim to dehydration caused by diarrhea. If the water is turbid, or cloudy, SODIS does not work since the sun's UV rays cannot penetrate the water effectively. This leaves millions of people without access to the least-expensive method of purifying drinking water. Our prior research has shown that adding common table salt to cloudy water decreases turbidity caused by pure clays (commonly found in well and lake waters) enough to make SODIS effective, while keeping the salt level within a healthy range. Water from areas with vertisol-type soil, which covers approximately 335 million hectares worldwide, is often clouded by the same type of clays that we have previously studied. Now, we must determine if all types and mixtures of vertisol soils can be cleared enough by table salt to render SODIS effective. Additional funding will allow us to test actual soil samples from around the world to see where else SODIS is feasible, and where public information campaigns sharing the SODIS-and-salt method should be concentrated.