Abstract <p>This study evaluates the variability of water quality in the Hirakud dam reservoir by analyzing thirteen key parameters. There exist significant seasonal variations in both reservoir and seepage water. The results indicate that most parameters, including pH, electrical conductivity (EC), and total dissolved solids (TDS), were elevated during the summer months due to factors such as geological composition, evaporation, and anthropogenic inputs from the Ib-Jharsuguda valley. The Langelier saturation index (LSI) indicates that reservoir water was corrosive during winter, spring, and summer, as it was unsaturated with CaCO₃, leading to potential concrete deterioration. Conversely, during the monsoon, CaCO₃ precipitation provided a protective layer, reduces the corrosiveness. The aggressive index (AI) corroborated these findings, showing moderate corrosiveness in winter, spring, and summer, and non-corrosiveness in the monsoon. The Ryznar stability index (RSI) further supported the LSI and AI results, highlighting seasonal stability and corrosivity, with CaCO₃ precipitation observed in the monsoon. Seepage water from the dam’s foundation gallery exhibits higher chloride and sulfate concentrations during summer compared to reservoir water. Elevated pH values indicated increased alkalinity and ongoing leaching from concrete, which may impact concrete integrity and rebar corrosion. Overall, while reservoir water quality meets standards, seepage water poses corrosion risks to concrete structures. Regular monitoring of concrete strength and rebar condition is recommended. Establishing a comprehensive water quality assessment system and extending the study period are essential for understanding long-term impacts and tracking water quality trends.</p>