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Providing good quality water in sufficient quantities is a major challenge in the world. The purpose of the study is to assess the quality of drinking water and the health risk of various population groups in the southern Baikal region (Siberia, Russia) under changing hydrological conditions. Lake Baikal is the largest freshwater body of water and is one of the sites protected by UNESCO. Materials and methods. An analysis of centralized and non-centralized water supply was carried out in the south-eastern part of the Irkutsk region, adjacent to Lake Baikal. The data used are from the Baikal (regional) Information Center for 2011–2022, and they include the results of monitoring the water quality of the centralized domestic and drinking water supply (CDW) with 140 thousand samples, and non-centralized domestic and drinking water supply (NDW) with 108 thousand samples. In all samples, 17 substances were determined. In addition, during the flood period, accompanied by additional water disinfection, trihalomethanes were determined in populated areas exposed to negative impacts. The quality of drinking water was assessed in comparison with the maximum permissible concentrations of substances (MPCs) approved by regulatory documents of Russia. An assessment of the characteristics of drinking water consumption by the population of the Baikal region was carried out, based on interview data from sample groups of the population. The assessment of the risk to public health, due to chronic oral intake of chemicals, was carried out using the values of the hazard coefficient (HQi), the hazard index (HI), individual carcinogenic risk (ICR), and population carcinogenic risk (PCR).Village residents more often use underground water sources (centralized and non-centralized). Residents of cities are provided with water from surface sources (Lake Baikal and the Angara River). Significant concentrations of iron, nitrates, and manganese were found in drinking water used by villagers. Average concentrations of iron - 2.25 mg/dl, manganese - 0.6 mg/dl, nitrates - 135 mg/dl were recorded in the water of underground springs in villages of the Irkutsk region. Among rural residents of the Irkutsk region, 60.8 % live in settlements with non-water supply systems, 28.4 % have mixed water supply.The non-carcinogenic risk for the adult and child population was calculated; HI > 1 was identified for the population using underground water sources. the non-carcinogenic hazard for the adult population, it was found that HI in the Irkutsk region slightly exceeded the standard value (1), amounting to 1.3, and for the child population - 1.6, the main contribution to the hazard index is represented by nitrates. For children of individual rural settlements of the Angarsk region HI = 1.38. The carcinogenic risk for water from underground sources reached in the range 1.56 × 10−5- 2.1 × 10−4 (in some settlements). Priority carcinogens were identified: arsenic (the contribution of which is 56.3–100 %), hexavalent chromium (29.9–35.8 %). A carcinogenic risk for city residents arises from increased disinfection during periods of microbiological contamination (floods, rains, high water levels), and it is associated with the formation of halogen-containing compounds. Conclusion: The need to strengthen the drinking water quality monitoring system in risk areas has been proven by increasing the number and frequency of sampling during flood periods.