Highlights: Public Health Relevance—How does this work relate to a public health issue? Microbiological contamination of drinking water, particularly Escherichia coli, is strongly associated with stunted growth and reduced height-for-age Z-scores in children aged 0–5 years, directly contributing to the global burden of child undernutrition that affects an estimated 149 million children. This systematic review synthesizes evidence from low- and middle-income countries (LMICs) where inadequate WASH infrastructure amplifies children’s vulnerability to contaminated drinking water, underscoring the urgent public health need for safe water access as a foundation of child health and development. Public Health Significance—Why is this work of significance to public health? This review provides a comprehensive synthesis of the evidence linking drinking water quality to both physical growth and cognitive development in early childhood, demonstrating that contaminated water not only causes stunting but may also impair neurodevelopmental outcomes—a dual burden with lifelong implications for educational attainment and economic productivity. The findings highlight that single-component water treatment interventions (e.g., chlorination alone) are insufficient to substantially improve child growth outcomes; integrated WASH-nutrition strategies addressing multiple exposure pathways are required, which has significant implications for the design and funding of public health programs aligned with Sustainable Development Goal (SDG) 6. Public Health Implications—What are the key implications or messages for practitioners, policy makers and/or researchers in public health? Policy makers and program implementers should prioritize integrated WASH and nutrition interventions over water-quality-only approaches, as combined strategies targeting water, sanitation, hygiene, and nutritional support have demonstrated greater benefits for child growth and cognitive outcomes across diverse LMIC settings. Researchers should address critical gaps in this field, including the limited evidence on chemical contaminants’ effects on child development, the need for longitudinal studies with standardized cognitive outcome measures, and the importance of conducting well-registered, prospective studies in diverse geographic settings to strengthen evidence for global policy translation. Access to safe drinking water is critical for child growth and development. However, microbial contamination is a constant threat in many low- and middle-income countries. The current systematic review sets out to examine the evidence of drinking water quality and the physical and cognitive development of children aged 0 to 5 years. The review authors conducted a comprehensive search of SCOPUS, EBSCO, PubMed, the Cochrane Library, and Google Search for cohort studies and clinical trials conducted in English between the years 2010 and 2025. Of 222 studies, 15 were included in the review and the majority were conducted in low- and middle-income countries The findings consistently demonstrate that microbiological contamination, predominantly by Escherichia coli (the primary water quality indicator examined across studies), is associated with an increased risk of stunting (odds ratio up to 4.14) and reductions in height-for-age Z-scores (HAZ) (by 0.29–0.57). There is currently limited evidence in the studies reviewed that suggests a correlation between the presence of unsafe drinking water and a decrease in cognitive development; however, the evidence is insufficient and warrants further study. Integrated water, sanitation and hygiene (WASH) and nutrition programs had promising growth results, which varied depending on the initial sanitation coverage of the target population, adherence to the intervention, and the overall design of the program. To sum up, contaminated drinking water negatively affects physical and cognitive development during early childhood. Comprehensive WASH–nutrition strategies need to be implemented to reduce this impact and further progress towards Sustainable Development Goal (SDG) 6. © 2026 by the authors.