Soft water attack plays a major role in the deterioration of aging dams. The present paper investigates the impact of water quality on the durability of one such aging dam by conducting chemical analysis and mineralogical studies. This study aims to investigate the risk of chemical damage originating from water quality on the structural durability of embankment. In continuation of this, a field study involving water samples at various sites of the embankment was carried out by the Central Soil and Materials Research Station team. To know the water quality of the reservoir, the study has been extended to the reservoir water, which offers a useful representation of overall water quality. Various parameters such as pH, temperature, conductivity, total suspended solids, total dissolved solids, total hardness, and total alkalinity were calculated. The test results indicate that the quality of seepage water is softer than reservoir water. In order to determine the intensity of water aggression on embankment, the results of water quality tests were analyzed using soft water aggression indices such as Langelier (LI), Ryznar (RI) and calcium carbonate saturation [pHs] and recommendations from other international standards like United States Bureau of Reclamation (USBR), International Commission on Large Dams (ICOLD). The paper also presents a systematic calculation of the Aggressive Index of the seepage water. The reservoir water quality has a harmful effect on the structure, which intensifies the formation of cracks on the spillway. Mineralogical study of different minerals leached out from the dam embankment was also investigated, basic chemical parameters mentioned above, and mineralogical studies further support the seepage assessment.