Diarrheal diseases kill two million children every year despite the availability of effective and inexpensive technologies to improve water quality and limit the spread of pathogens. There is a growing literature on the effectiveness of such technologies but important gaps remain in understanding the demand for these products and the adoption decision. This review expands upon and complements several existing summary articles by focusing on willingness to pay for cleaner water. Willingness to pay can be measured by price randomizations that induce people to reveal their valuation in real purchase decisions or by other methods such as contingent valuation exercises in hypothetical situations and discrete choice analysis. The review conducts a systematic search for experimental evidence on willingness to pay for cleaner water.