Many effective health products and behaviors available through the private market are not widely adopted in less developed countries. For example, fewer than 10% of households in our Kenyan study area treat their water with dilute chlorine. Using a suite of randomized evaluations, we find that information and marketing interventions do little to boost use of chlorine. However, chlorine take-up is highly sensitive to price, convenience and social context, with more than half of households using chlorine when an individually-packaged supply is delivered free to the home. The highest sustained take-up is achieved by combining free, convenient, salient, and public access through a point-of-collection chlorine dispenser system and a local promoter. More than half of households treat their water and this use continues 30 months later even though promoters are paid only for the first six months. The estimated long-run costs of this intervention at scale, including administrative costs, are between $0.25 and $0.50 per person per year.