Fuzzy multi criteria decision analysis for drinking water suitability in urban lake groundwater systems in Chennai India

Urban lake–groundwater systems in Chennai, India, face severe contamination challenges due to rapid urbanization, seawater intrusion, and anthropogenic inputs, while conventional water quality assessment approaches often fail to adequately account for uncertainty in ranking outcomes. To address this limitation, the present study applied fuzzy-based multi-criteria decision analysis techniques alongside conventional water quality index and classical multi-criteria decision-making approaches. A total of 30 water samples collected from three major lakes and adjacent groundwater sources were analyzed for physicochemical parameters using standard analytical procedures. The results indicate that lake waters generally comply with drinking water standards, reflecting the beneficial influence of rainfall recharge and dilution processes, whereas groundwater quality is considerably affected by seawater intrusion, prolonged water–rock interaction, and contamination from sewage infiltration and agricultural activities. Hydrogeochemical facies analysis revealed predominantly alkaline waters characterized by calcium–magnesium and sodium–chloride types, while hydrochemical interpretation suggested strong hydraulic connectivity between lakes and adjacent aquifers. Comparative evaluation demonstrated that fuzzy decision-making approaches produced more consistent and uncertainty-aware rankings than conventional methods, thereby providing a more reliable framework for drinking water suitability assessment. The proposed methodology offers a practical and reproducible approach for groundwater quality evaluation in data-limited urban environments and can be applied to similar lake–aquifer systems worldwide. The findings contribute to sustainable water resource management, urban resilience planning, and the achievement of global water sustainability objectives.