Evaluating non potable groundwater quality in estuarine Islands of Karnataka using GIS and WQI

Fresh groundwater is scarce on estuarine islands due to seasonal fluctuations in the groundwater table and tidal influence. Larger inhabited islands face increasing concerns over access to safe water for household activities. This study evaluates the groundwater quality on Mudukudru Island, one of the largest in the estuary of the Swarna-Sita River system in Udupi district, Karnataka. A total of 43 wells used for non-potable domestic purposes were analyzed during the pre-monsoon season (2021-2022) using a Hanna HI9829 multiparameter testing kit. The Weighted Arithmetic Water Quality Index Method was applied to assess water quality based on four physical parameters (Total Dissolved Solids, Electrical Conductivity, Salinity, Temperature), three chemical parameters (pH, Oxygen Reduction Potential, Dissolved Oxygen), and one biological parameter (Most Probable Number of coliform bacteria). GIS-based spatial maps were developed to visualize distribution patterns. The overall WQI results indicate that approximately 30% of the island's groundwater falls under the "unsuitable" category. Traces of coliform bacteria were recorded in all samples, indicating that the groundwater is not suitable for drinking without treatment. The findings underscore the need for water purification, regular monitoring, and sustainable management of groundwater used for non-potable household use.