Background In 2024, an estimated four billion people lacked access to safely managed drinking water, with the greatest risks in low- and middle-income countries, particularly for vulnerable groups such as young children and pregnant women.

Methods This paper analyzes data from 59,633 households in 25 countries across Sub-Saharan Africa, Latin America, and Asia to examine E. coli contamination in source water and household responses through water treatment. It investigates whether households are more likely to treat water when source water is contaminated and how treatment relates to E. coli levels in stored drinking water.

Findings The study finds that 78 percent of households do not treat their water, while 20 percent rely on sources with high E. coli contamination (>100 MPN/100ml). The presence of E. coli is associated with a modest increase in water treatment—typically three to five percentage points, de-pending on the contamination level—driven by greater use of chlorine products or straining/settling methods. While water treatment is linked to lower contamination levels in stored drinking water, a large share of households that treat their water still face moderate to high E. coli contamination risk at the point of consumption.

Interpretation These findings highlight that the key challenge is not only whether households treat their water, but whether they do so properly and consistently. Observational evidence from real-world conditions points to the need for more WASH strategies that go beyond promoting access to treatment, ensuring its correct application to deliver safe drinking water.

Funding No funding was received for this research.

Evidence Before This Study Previous research on water quality and health in low-income countries has primarily focused on access to water infrastructure or small-scale trials of water treatment interventions. Only recently have nationally representative surveys begun testing for microbial contamination at the point of use within households. Analyses of data from the UNICEF Multiple Indicator Cluster Surveys (MICS) have shown that E. coli contamination is widespread, even in improved water sources, highlight-ing the need for effective household-level treatment (Husein, Nounkeu, Armah, & Dharod, 2023; Joseph, Haque, Moqueet, & Rong Hoo, 2019; Kandel, Kunwar, Lamichhane, & Karki, 2016). Using evidence from 27 countries, Bain, Johnston, Khan, Hancioglu, and Slaymaker (2021) demonstrate that contamination frequently persists at the point of consumption.

This study is among the first to examine household water treatment behavior in direct relation to measured E. coli contamination, using large-scale, nationally representative data.

Added value of this study This study offers a large-scale multi-country analysis of drinking water safety and household re-sponses, using data from 59,633 households in 25 countries in Sub-Saharan Africa, Latin America, and Asia. In contrast to research that relied on proxy indicators of contamination, this study uses direct microbiological testing of source and drinking water for E. coli contamination at a large scale. By pooling multiple nationally representative DHS surveys, the study achieves broad external va-lidity. The paper documents the share of households exposed to contamination at the source and the proportion who treat their water among those at risk, as well as how water treatment practices relate to lower levels of E. coli in stored drinking water. This framework offers new, policy-relevant evidence grounded in real-world conditions. It advances our understanding of the proportion of people treating water, among those exposed to high water contamination risk, and how effectively these practices result in safe drinking water.

Implications of all the available evidence Despite well-documented health risks from waterborne pathogens (Nataro & Kaper, 1998), treat-ment adoption remains low even among highly exposed households. Furthermore, the weak rela-tionship between existing treatment methods and E. coli-free drinking water highlights the need for more scalable and effective WASH interventions.

The collective evidence underscores that ensuring safe drinking water in LMICs requires not only improving access to water sources but also promoting and sustaining effective water treatment at the household level. The findings from this study, in line with prior knowledge, highlight that many households remain exposed to fecal contamination because they do not consistently treat their water, do not have the means to measure the contamination level, or because treatment is not always effective. This implies that water, sanitation, and hygiene (WASH) policies must go beyond simply encouraging water treatment behavior: they should ensure that households have the means, knowledge, and motivation to treat water properly and consistently. By emphasizing correct and routine use of household water treatment, alongside improvements in source water quality, public health programs can more effectively protect families from waterborne illnesses and advance progress toward truly safe drinking water for all.

The authors have declared no competing interest.

The author(s) received no specific funding for this work.

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