The Relationship between Chlorine Residuals in Drinking Water, Gut Microbiota Disorders, and Cancer Development

Residual chlorine in centralized urban drinking water is essential for disinfection but may pose health risks associated with gut microbiota imbalance and cancer development. This article analyzes 21 scientific studies published between 2020 and 2025 to examine the effects of chlorine (0.2–1.0 mg/L) and wastewater admixture on gut bacteria and cancer risk. The findings indicate that chlorine slightly alters gut microbiota composition, increases antibiotic resistance by 5–7 times, and elevates colorectal cancer risk by 1.3–1.8 times through trihalomethanes (THMs). In children, Akkermansia and Escherichia populations increase, while beneficial bacteria decrease, leading to dysbiosis and inflammation. In Uzbekistan, chlorination has reduced diarrhea incidence by sixfold; however, the impact of municipal tap water quality on gut health and cancer risk remains unstudied. The paper recommends improving water filtration systems, strengthening monitoring, and conducting further research in this field.