Turkalj M, Drkulec V, Haider S, et al. - This study was undertaken to determine if bacterial load in drinking water was correlated with altered risk of allergic diseases. Participants in the study were 1,110 schoolchildren (aged 6‐16 years) between 2011 and 2013 in Požega‐Slavonia County in Croatia, where the authors capitalized on a natural experiment whereby people receive drinking water through public mains supply or individual wells. Data on microbial content of drinking water for all participants were obtained. Five hundred eighty-five children were randomly selected for more detailed assessments, including skin prick testing. Among children with individual supply, cumulative bacterial load in drinking water was higher, and lifetime prevalence of allergic diseases was significantly lower. In quantitative analysis, the risk of allergic diseases decreased significantly with an increase in the bacterial load in drinking water in the first year of life. Findings suggested that high commensal bacterial content can protect against allergic disease in drinking water.