Abstract: The Shendong Mining Area is endowed with abundant coal resources yet faces severe water scarcity. The successful application of underground reservoir technology has preserved a significant amount of mine water resources in the region. Gaining insight into the hydrochemical properties and potential health risks of water in these underground reservoirs is a critical prerequisite for the protection and utilization of water resources in the mining area. Taking the underground reservoir group in the Shendong Coal Mine as the research object, this study collected and tested samples of the inflow and outflow mine water from the reservoir group. By adopting methods including the Entropy-weighted water quality index method, hydrogeochemical analysis, and correlation analysis, the hydrochemical characteristics, water-rock interaction patterns, and potential health risks of the mine water in the underground reservoir group were analyzed. The results indicate that after purification and regulation by the underground reservoirs, significant changes occurred in the water quality of the inflow and outflow. The mass concentrations of total dissolved solids(TDS), calcium ions, magnesium ions, sulfate ions, and chloride ions increase markedly, while the mass concentrations of indicators such as pH, ammonia nitrogen, potassium ions, iron, and fluoride decrease to varying extents. The hydrochemical type of inflow water is HCO₃·SO₄−Na, whereas the outflow water gradually transforms into HCO₃·SO₄−Ca. The distribution characteristics of the inflow and outflow water quality in the underground reservoir group are related to the hydrogeological conditions. The primary drivers for the changes in outflow water quality are the dissolution of water-rock interactions, ion exchange, and cation alternation adsorption within the underground reservoirs. Overall, the quality of the inflow and outflow mine water in the underground reservoir group of the Shendong Mining Area is excellent, with the outflow water quality generally superior to the inflow water quality. The purification effect of water-rock interactions in the underground reservoirs exerts a positive influence during the migration of mine water. From the perspective of health risk assessment, the health risks caused by the inflow and outflow water of the underground reservoir group through skin infiltration are negligible (the non-carcinogenic health risk HI value is less than 1). However, the inflow and outflow water of the reservoirs may pose potential health threats to miners and surrounding residents via drinking water intake, with iron (Fe) and manganese (Mn) in industrial wastewater identified as the main risk factors.The findings of this study provide a scientific basis for the safe utilization and health risk prevention and control of mine water in coal mine underground reservoirs, offering significant guidance for ensuring regional water resource security and public health in the Shendong Mining Area.