Chlorine (Cl^-) is used as a disinfectant of drinking water and drinking water distribution networks in Petropavlovsk, Kazakhstan. The disinfectant, interacting with fulvic and humic acids, forms disinfection by-products (DBPs), particularly, trihalomethanes (THMs). THMs might be harmful to the population, as it may cause cancer and non-cancerous diseases. As a result, the current study was focused on the assessments of the lifetime risk of cancer and non-cancerous diseases associated with THMs in Petropavlovsk community. To calculate multipathway lifetime risks of cancer and non-cancerous diseases associated with THMs we used combined United States Environmental Protection Agency (US EPA) and scientific methods. The mean concentrations of CHCl3, CHBr3, and CHCl₂Br in drinking water were 18.41 μg/L, 48.7 μg/L, and 6.15 μg/L, respectively. The mean lifetime risk of cancer associated with THMs in drinking water was 3.83 × 10^-5. The total lifetime risk of non-cancerous diseases associated with THMs was 2.13 × 10^-1. The total lifetime risks for cancer from the three routes for the three THMs at 50^th and 95^th percentile scenarios were higher than the risk of the US EPA recommendation of 1.00 × 10^-6, while the total lifetime risks of non-cancerous diseases associated with THMs were lower than the US EPA recommendation of 1.