The importance of waterborne gastrointestinal illness throughout the developing world, the existence of a cheap and effective intervention (SODIS), the concurrent limited dissemination program for SODIS, the need for a controlled evaluation of the effectiveness of SODIS under actual field conditions, and the experience of our tri-national collaborative research team in successfully conducting large scale drinking water intervention and observational studies in both the United States and the developing world encourage us to propose the following randomized controlled trial in which our specific aims are to: