Our estimate suggests that chlorination reduces all-cause mortality in children under five by about 14%. After adjustments, including those related to local diarrhea mortality rates and differences between the interventions used in the trials versus in the charity context, we estimate that two types of chlorination interventions we’re currently assessing—Dispensers for Safe Water and in-line chlorination—reduce all-cause mortality in under-five children by 6 to 11%, as described in the "What led us to update" section.
"Diarrhoeal disease is the second leading cause of death in children under five years old." WHO, "Diarrhoeal disease," 2017.
The Institute for Health Metrics and Evaluation's Global Burden of Disease (GBD) tool estimates that in 2019, enteric infections caused 15.3% of all deaths in under-five children in sub-Saharan Africa (see here).
 Water chlorination has been used in major cities in the United States since the early twentieth century: "Following the demonstration of chlorine's use for disinfection in 1908, most major cities began water chlorination within the next decade." Cutler and Miller 2005, p. 3.
See, for example, Evidence Actions's Dispensers for Safe Water as one charity set up to implement chlorination.
In our cost-effectiveness analysis we estimate that in-line chlorination in Kenya costs about $1.68 per person served and that Dispensers for Safe Water costs between $1.22 and $1.87 per person served, depending on the country.
 This assumes a 1:1 relationship between reductions in diarrhea morbidity and reductions in diarrhea mortality. We describe further and provide sources in our water quality intervention report: "The most recent Cochrane meta-analysis of water quality interventions reports that chlorination interventions reduce the risk of diarrheal illness by 23% in low-income settings. GBD estimates that 14.5% of all-cause mortality in children under age five in countries with low socio-demographic index is caused by enteric infections. Together, these estimates imply that chlorination might reduce all-cause mortality by 3.3%." GiveWell, "Water quality interventions," 2022.
 Michael Kremer co-founded Deworm the World, which later became part of Evidence Action. Additionally, Stephen Luby, a co-author of this paper, is on the Board of Advisors for Evidence Action (note: this is separate from Evidence Action’s Board of Directors).
 Kremer and his team's initial estimate was slightly higher, 28 to 30%. These are the estimates we currently cite in our water quality report: "Depending on the method used to pool results, the analysis reports that water quality interventions reduce the odds of all-cause mortality in children under five by 28% (95% confidence interval, 8% to 45%) or 30% (95% credible interval, 8% to 51%)." Since we wrote the intervention report, Kremer et al. (2022, p. 1) have adjusted their estimate to account for the greater uncertainty of implementation in a new context: "Taking into account heterogeneity across studies, the expected reduction in the odds of all-cause child mortality in a new implementation is 25%." In other words, the new estimate is not simply a statistical description of previous RCTs, but a prediction of what one would expect from conducting a new trial.
 Beyond reductions in under-five mortality, the current analysis also incorporates benefits from reduced mortality in people five and over, as well as development benefits (increases in consumption resulting from reduced illness). See our analysis here. The 2017 version of our Dispensers for Safe Water CEA modeled only reductions in under-five mortality.
We use GiveDirectly's unconditional cash transfers as a benchmark for comparing the cost-effectiveness of different funding gaps, which we describe in multiples of "cash." Thus, if we estimate that a funding gap is "10x cash," this means we estimate it to be ten times as cost-effective as unconditional cash transfers. As of this writing, we have typically funded opportunities that meet or exceed a relatively high bar: 8x cash. We also consider funding opportunities that are between 5 and 8x cash.
Note that our cost-effectiveness analyses are simplified models that do not take into account a number of factors. There are limitations to this kind of cost-effectiveness analysis, and we believe that cost-effectiveness estimates such as these should not be taken literally due to the significant uncertainty around them. We provide these estimates (a) for comparative purposes to other grants we have made or considered making, and (b) because working on them helps us ensure that we are thinking through as many of the relevant issues as possible.
 Evidence Action is the parent organization of one of our top charities, Deworm the World Initiative. We've also directed funding to its Accelerator program and the since-discontinued No Lean Season.
 We describe this grant, which will be funded by Open Philanthropy, as "up to $64.7 million" because $15.9 million is exit funding that will be released only upon our decision to withdraw support from the program. More details on this grant will be available in a forthcoming grant page.
 Based on our rough estimates of long-term room for more funding in countries DSW might expand to where we estimate the program would be at least eight times as cost-effective as unconditional cash transfers. See here in our room for more funding analysis.
 See GiveWell, "Water quality interventions," 2022: "In-line chlorination is a technology for automatically disinfecting water at shared water collection points in low-income settings with unsafe water." See Pickering et al. 2019 for a more detailed description of an in-line chlorination system.