A water quality intervention that consists of water treatment, safe storage, and community education was field tested in Kitwe, Zambia. A total of 166 intervention households were randomly selected from one community and 94 control households from another. Baseline surveys were conducted and the intervention was distributed. Weekly active diarrhea surveillance, biweekly water testing, and a follow-up survey were conducted. Compliance was high in intervention households: 97% reported using disinfectant and 72-95% had measurable chlorine in their water in biweekly testing. The percentage of intervention households storing water safely increased from 41.5% to 89.2%. Stored water in intervention households was significantly less contaminated with Escherichia coli than water in control households (P < 0.001). Diarrheal disease risk for individuals in intervention households was 48% lower than for controls (95% confidence interval = 0.3, 0.9). This intervention is a useful tool for preventing waterborne diseases in families in developing countries who lack access to potable water.