Diarrhea is one of the leading causes of death for children under five, killing more than 400,000 children every year.¹“Diarrhoeal disease is the third leading cause of death in children under 5 years old and is responsible for killing around 443 832 children every year.” World Health Organization, “Diarrhoeal disease,” 2024. GiveWell has funded several programs to prevent and treat diarrhea, and we recently expanded our work by making a grant to support the implementation and evaluation of WASHmobile in the Democratic Republic of the Congo (DRC) and South Sudan. The program, which was developed by Johns Hopkins University, delivers water treatment supplies and hygiene messaging to households at the highest risk of diarrheal disease. It has shown promising results in randomized controlled trials (RCTs) but hasn’t yet been implemented at scale in the challenging settings where the need is greatest.

In this episode, GiveWell co-founder and CEO Elie Hassenfeld speaks with Senior Program Officer Erin Crossett, who leads GiveWell’s water research subteam, about the grant. They discuss how the program works, what prior research tells us about its potential, the significant uncertainties involved, and what GiveWell expects to learn.

Elie and Erin discuss:

• How WASHmobile works: When someone in a household has diarrheal disease, others in the household are at much higher risk. To reduce this risk, WASHmobile first identifies children who have been hospitalized with severe diarrhea. A health worker visits their family to provide handwashing supplies and chlorine tablets to disinfect water, then follows up with phone reminders about safe water practices. Because household members often share the same water source and live in close quarters, treating water and improving hygiene during this critical window can prevent further infections and deaths. Trials of more intensive versions of this program found reductions in diarrheal disease of roughly 60%. Our grant also includes a second, lower-cost component that sends SMS alerts and digital chlorine vouchers to people living near detected outbreaks.
• Navigating uncertainty in fragile contexts: WASHmobile is being implemented in South Kivu (DRC) and Jonglei State (South Sudan) by Tearfund, which is partnering closely with the countries’ ministries of health. Because of active armed conflict, severe flooding, and large displaced populations, these areas are challenging for health program implementation. GiveWell is funding a version of the program that is less intensive than the one studied in trials, with shorter duration and less intensive follow-up, and we have discounted expected effects accordingly. Even with those adjustments and a substantial probability of program failure built into our modeling, we estimate the program could be highly cost-effective because disease burden in these areas is so high.
• Building learning into the grant: Roughly half of the grant funds implementation, and half is dedicated to evaluation and data collection. In DRC, GiveWell is funding Johns Hopkins University, in partnership with Catholic University of Bukavu, to conduct a randomized controlled trial alongside implementation to measure the program’s effect on hospital admissions for diarrhea among children under five. The trial will also help test one of the key assumptions in our cost-effectiveness model: that the families this program targets are actually at higher mortality risk than the general population. In South Sudan, where a full trial wasn’t feasible, we’re funding mortality surveys and operational monitoring to better understand baseline mortality and whether the program is being implemented as intended.

This grant reflects how GiveWell’s growing team capacity allows us to do more than scale up proven programs; it also enables us to investigate new, cost-effective ways to save and improve lives beyond our traditional grantmaking portfolio. In addition, our growing capacity means we’re increasingly able to help bridge the gap between academic research and real-world implementation—funding promising programs alongside the rigorous evaluation needed to determine whether they should be scaled further.

Visit our All Grants Fund page to learn more about how you can support this work, and listen or subscribe to our podcast for our latest updates.

This episode was recorded on June 10, 2026, and represents our best understanding at that time.