Impact on childhood mortality of interventions to improve drinking water, sanitation, and hygiene (WASH) to households: Systematic review and meta-analysis

**Background:** Diarrhoeal diseases and respiratory infections kill approximately 4.1 million people annually, with half of these deaths occurring in children under 5 years old, primarily in low- and middle-income countries (L&MICs) lacking adequate water, sanitation, and hygiene (WASH). Previous estimates of WASH health impacts relied on self-reported morbidity, which is prone to bias. This study used reported mortality—considered less biased—to estimate WASH intervention effects on childhood mortality.

**Methods:** A systematic review and meta-analysis was conducted following a published protocol (PROSPERO CRD42020210694). Searches of 11 academic databases, trial registries, and organizational repositories were performed for studies published through March 2020. Eligible studies included RCTs and NRSI of WASH interventions in L&MICs under endemic disease circumstances. Two authors independently collected data, including mortality data from participant flow diagrams. Risk of bias was assessed using adapted Cochrane tools. Meta-analysis used odds ratios (OR) with 95% confidence intervals. Heterogeneity was assessed via I-squared and tau-squared statistics. Meta-regression examined effect moderators including WASH technology, counterfactual conditions, participant age, season, and follow-up duration.

**Key Results:** From 13,500 deduplicated records, 35 studies (24 RCTs, 11 NRSI) were included, incorporating 2,600 deaths across 48 treatment arms. WASH interventions significantly reduced all-cause childhood mortality by 17% (OR=0.83, 95% CI 0.74–0.92; 38 estimates; I-squared=16%). Diarrhoea mortality was reduced by 45% (OR=0.55, 95% CI 0.35–0.84; 10 estimates; I-squared=43%). Water supply interventions reduced all-cause mortality by 34% (OR=0.66, 95% CI 0.50–0.88; 7 estimates). Community-wide sanitation reduced all-cause mortality by 21% (OR=0.79, 95% CI 0.66–0.95; 8 estimates), while household-level sanitation showed no effect (OR=1.07, 95% CI 0.83–1.36; 4 estimates). Hygiene promotion reduced all-cause mortality only when water supply was also improved (OR=0.71, 95% CI 0.56–0.90; 11 estimates) versus no effect without improved water (OR=1.02, 95% CI 0.84–1.23; 6 estimates). Household water treatment showed no significant effect on all-cause mortality (OR=0.93, 95% CI 0.75–1.14; 15 estimates). For diarrhoea mortality, effects were larger when counterfactual groups lacked improved water and sanitation (OR=0.31, 95% CI 0.16–0.60) versus when they had improved facilities (OR=0.78, 95% CI 0.62–0.98; p<0.01 for difference). Meta-regression (R-squared=76%) showed larger effects for children under 5, during summer/rainy season, and with shorter follow-up. No effect was found for participants aged over 5 years (OR=1.05, 95% CI 0.93–1.19; 7 estimates). No studies were at low risk of bias; 40% were at moderate risk.

**Clinical Implications:** WASH interventions—particularly improved water supply and community-wide sanitation—substantially reduce childhood mortality in L&MICs. Water supply improvements enable domestic hygiene practices critical for reducing both diarrhoeal and respiratory infections. Community-wide sanitation reduces faecal-oral pathogen transmission. Hygiene promotion is effective only when sufficient water is available. Interventions are most impactful in high-mortality, high-contamination settings. These findings support prioritizing water supply and community-wide sanitation during the UN International Decade for Action on Water (2018–2028). Transparent reporting of participant flows in trials is essential for ongoing evidence synthesis.