DescriptionUrbanization sanctions the use of sanitation and health practices that have helped to control the transmission of infectious diseases. One of the widely used methods of disinfection is water chlorination, which achieves the purpose of killing pathogenic microbes, but may could also affect the human microbiome. In this pilot study, experiments were conducted in mice, to investigate the effects of chlorinated water consumption from early life, on growth and microbiome development. The experiment involved 10 pregnant dams, 5 in each group, and it was repeated twice (cohort 1 and 2). Body weight changes were measured, and fecal samples were collected weekly for microbiome structure determination. The results showed that there was a significantly higher developmental weight gain in mice (both males and females) that consumed chlorinated water, and the effect was consistent in the two cohorts. The effect was observed after weaning, when the young animals started drinking the chlorinated water. Chlorination significantly altered the microbiome, lowering fecal alpha diversity. The results suggest that drinking chlorinated water at early ages may significantly affect development, by microbiome-meditated mechanisms, with important implications for human health.