Existing strategies for improving global access to safe drinking water have met only limited success. We consider an unglamorous and often neglected dimension of drinking water infrastructure provision: cleaning. We randomly assigned caretakers of community wells to participate in a training workshop about how to clean wells. Thirteen to seventeen months later, wells with caretakers assigned to receive training have negligible rates of contamination with Escherichia coli (13 months: 2%; 17 months: 4%), while control wells have substantial rates of E. coli contamination (13 months: 14%; 17 months: 19%). Rates of contamination with any coliform bacteria are almost halved (13 months: control 55%, treated 30%; 17 months: control 77%, treated 46%). We estimate the cost of preventing exposure to coliform bacteria in drinking water to be US$0.89 per person and that, if scaled up, each US$2376 spent on the intervention could avoid the death of a child.