Geochemical Evaluation and Potability of Groundwater in a Hard Rock Terrain: A Case Study from the Karaipottanar Sub-Basin, Southern India

Groundwater serves as the primary source of water for domestic, agricultural, and industrial use in many countries. Effective water resource management requires the implementation of strategies to protect aquifers from contamination. Monitoring groundwater quality is crucial for ensuring environmental sustainability and public health, as it provides essential data for informed decision-making. The geochemical characteristics of groundwater significantly influence the suitability and sustainability of aquifer systems as water sources. This study aims to evaluate the groundwater chemistry of a hard rock aquifer in the Karaipottanar sub-basin, Tamil Nadu, India, and to assess its suitability for drinking, domestic, agricultural, and industrial applications. A total of 44 groundwater samples were collected from various geological formations like charnockite, fissile hornblende biotite gneiss, granitic/acidic rocks, and alluvial deposits. Physicochemical parameters such as pH, total dissolved solids (TDS), and major ions were analyzed and compared with the Bureau of Indian Standards (BIS, 2012) guidelines. The Drinking Water Quality Index (DWQI) was employed to evaluate the water’s fitness for human consumption. To assess irrigation suitability, analytical tools such as the Wilcox diagram, USSL diagram, Sodium Adsorption Ratio (SAR), and Permeability Index (PI) were used. For domestic and industrial suitability, the Langelier Saturation Index (LSI), Ryznar Stability Index (RSI), and Corrosivity Ratio (CR) were applied and interpreted based on standard classifications. Hydrogeochemical processes were further investigated using Gibb’s and Piper trilinear diagrams. Additionally, Principal Component Analysis (PCA) was conducted to identify the underlying relationships among groundwater quality parameters and to understand the complexity of the hydrogeochemical system in the study area.