The proposed study is a 12-month double-blinded, randomized, placebo-controlled trial to determine if the impact of treating water with chlorine at the household level is effective in preventing diarrhea among young children. For more than a century, chlorine has be used to treat water in municipal systems in developed countries. Lack of infrastructure has prevented its use in lower-income settings. NaDCC is a tablet form of chlorine that has been used for more than 30 years in emergencies and has recently been approved for routine treatment of drinking water by the WHO and US Environmental Protection Agency. The placebo will consist of the food-grade ingredients in the effective tablet, without the chlorine. Study participants will be supplied with tablets (intervention or placebo) and instructed to use the same to treat their water daily. Monthly follow-up visits will assess diarrhoea morbidity and weight-for-age Z scores in <5s. Chlorine residual and bacteriological quality of water stored in the home will be measured each month. The study will also assess the impact of the intervention on absenteeism from school and work and on health care expenditure for diarrhoea.