Fill a clear plastic bottle with contaminated water. Leave it in sunlight for six hours. Then you have clean water! Or do you?
Solar Water Disinfection (SODIS) is widely promoted as one way to lower the incidence of diarrheal disease in developing countries that have limited access to clean water. The UV-A radiation of the sun and increase in the water temperature are supposed to inactivate microorganisms.
Recent studies report that SODIS isn't as effective as claimed. SODIS is not reducing diarrhea as it should if the water is disinfected. It could be that people are disinfecting only some of their water. Or it could be that SODIS just isn't that effective.
Imagine if before you could use any water, that you needed to fill a bottle and leave it in the sun for six hours? What happens when it is cloudy? Not so good for people who live in places like Seattle.
Read the SODIS pamphlet to find out more.