As we continue to grow, GiveWell seeks to maximize both the cost-effectiveness of the funding we direct and the likely room for more funding of the programs we support. We think we’ve identified a category of interventions that rates really well on both: water treatment, such as chlorination.
This is a major update for us. Before 2020, based on the available evidence, we didn’t believe that water quality interventions had a large enough effect on mortality to make them a competitive target for funding. We’ve since seen new evidence that has led us to significantly increase our estimate of the mortality reduction in young children that’s attributable to these interventions: a 14% reduction in mortality from any cause,[1] up from around 3%.
Though we have remaining uncertainties about these numbers, we’ve substantially updated our view of the promisingness of water treatment. Where we previously found that Evidence Action’s Dispensers for Safe Water program was about as cost-effective as unconditional cash transfers, we now believe it’s about four to eight times as cost-effective, depending on the location. That was a primary factor in our decision to recommend a grant of up to $64.7 million to Dispensers for Safe Water in January 2022.
We’re sharing this news in brief form before we’ve published a grant page, because we’re excited about the potential of this grant and what it represents. It’s an area of work we haven’t supported to a significant degree in the past, but one that we now think could absorb hundreds of millions of dollars in funding for cost-effective programming.
The problem and the intervention
In low-income settings, contaminated water is a major cause of diarrhea, a leading cause of death in children under five years old.[2] Several interventions exist to either purify water or protect it from contamination in the first place, but chlorination has a number of features that made it an attractive intervention for us to explore: it is inexpensive and widely used, several charities are already set up to implement it, and the technology behind it is well established.[3]
Chlorine is well-known as a disinfectant; it reacts with disease-causing microorganisms in water, inactivating viruses and bacteria.[4] There is evidence that chlorination programs, such as distributing chlorine to households, reduce diarrhea in children, but there had been scant evidence that such

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