Assessment of Spatio-Temporal Changes in Groundwater Quality Using Water Quality Index and Its Irrigation Suitability in Puducherry Region, Southeast India

Groundwater sustains life in Puducherry coastal regions but faces threats from urbanization and land- use change. The study evaluated 70 groundwater samples in 2022, considering their suitability for drinking and irrigation purposes using water quality index, Canadian council of ministers of the environment-water quality index, and irrigation indices like sodium adsorption ratio, Percent Sodium, permeability index, Kelly's ratio, and residual sodium carbonate. Sentinel-2Asatellite images indicated that urban areas increased from 104.7 km² (35.1%) in 2010 to 105.7 km² (35.4%) in 2024, while agricultural land decreased marginally, mirroring urban pressure. Approximately 77.1% of the groundwater samples belonged to Fair to Marginal categories for drinking, and just 1.4% was rated Excellent under canadian council of ministers of the environment-water quality index. Salinity and nitrate were of primary concern, particularly in urbanised areas such as Solai Nagar and Kuruchikuppam, where water quality had been rated as Poor. For irrigation, 57.1% of pre-monsoon and 65.7% of post-monsoon samples were of the C3S1 class, reflecting low sodium hazard but high salinity, whereas 4.3% of pre-monsoon and 1.4% of post-monsoon samples encountered medium sodium hazard with very high salinity (C4S2). Kelly's Ratio was greater than 1 in 21.4% of pre-monsoon and 34.3% of post-monsoon samples, reflecting sodicity risks, while 98% of the samples had safe residual sodium carbonate values less than 2.5 meq/L. Regions with high urbanisation or intensive farming always exhibited high sodium adsorption ratio, Percent Sodium, and electrical conductivity, affirming a real correlation between land-use /land cover patterns and decreasing groundwater quality. To prevent these risks, the study suggests combined land-water planning, strict wastewater control, and the promotion of sustainable irrigation practices to ensure Puducherry's water resources and agricultural yield.