Geochemical characterization of groundwater and its suitability for drinking in the hard rock terrain of the Karaipottanar sub basin Southern India

Groundwater is the main source of water for domestic, agricultural, and industrial needs in many parts of the country, and its geochemical characteristics play an important role in determining the suitability and long term sustainability of aquifer systems. This study evaluates the groundwater geochemistry of the hard rock aquifer in the Karaipottanar sub-basin, Tamil Nadu, and assesses its suitability for drinking, domestic, agricultural, and industrial purposes. A total of 44 groundwater samples were collected from different geological formations such as charnockite, fissile hornblende–biotite gneiss, granitic/acidic rocks, and alluvial deposits. The physicochemical parameters were analyzed and compared with BIS (2012) standards, and the Drinking Water Quality Index (DWQI) was used to assess drinking suitability. Irrigation suitability was examined using the Wilcox and USSL diagrams, Sodium Adsorption Ratio (SAR), and Permeability Index (PI). Domestic and industrial suitability was evaluated using the Langelier Saturation Index (LSI), Ryznar Stability Index (RSI), and Corrosivity Ratio (CR). Hydrogeochemical processes were interpreted using Gibbs and Piper diagrams, and Principal Component Analysis (PCA) was carried out to identify the major controlling factors of groundwater chemistry. The results show that the central part of the basin is not suitable for most uses due to high mineral dissolution, strong rock–water interaction, and local anthropogenic influences, as reflected in the hydrogeochemical diagrams and PCA.