This study investigates the influence of rainfall on hydrogeochemistry in the hard rock terrain using GIS and remote sensing techniques. In hard rock regions, with limited porosity and permeability, hydrogeochemical processes play an essential role in groundwater recharge and quality. A total of 43 groundwater samples were collected from the field for major and minor ion analysis before and after the monsoon. This research utilizes geospatial technologies to analyse groundwater chemistry’s spatial and temporal variations in response to rainfall. By integrating remote sensing data, hydrogeochemistry assesses the correlation between rainfall and its impact on groundwater quality, such as pH, electrical conductivity, and major and minor ion concentrations. High concentrations of major and minor ions in drinking water can negatively affect human health. In the study area, hydrochemical parameters are reasoned to increase due to silicate weathering, rainwater recharge, and agricultural activities. This work identifies areas with significant hydrogeochemical changes during pre-monsoon and post-monsoon, which may indicate enhanced recharge or contamination processes. Groundwater’s primary hydrochemical facies have been classified as Ca-HCO3, Mixed Ca–Mg–Cl, and Na–Cl types. Temporal variations in groundwater quality are significantly impacted by rainwater recharge and rock types. The result of this study highlights the importance of rainfall as a driving factor in altering the hydrogeochemistry in hard rock terrains. This research provides valuable insights for water management, particularly in regions where groundwater is a primary water source. The use of GIS and remote sensing techniques proves to be an effective approach for assessing spatial groundwater quality in difficult geological settings.