Revealing Hidden Groundwater–Water Quality Nexus Relationships Using Multivariate Controls: Evidence from Vadodara, Western India

Groundwater level fluctuations are frequently used as a standalone indicator of groundwater stress, yet their ability to explain water quality variability remains limited (Famiglietti, 2014). This study evaluates groundwater-water quality nexus relationships in Vadodara district, western India, by integrating groundwater level change with key hydrogeochemical parameters. Using annual datasets (2014–2021) for nitrate (NO₃⁻), fluoride (F⁻), and electrical conductivity (EC), both bivariate and multivariate regression models were developed. Uncontrolled models show negligible explanatory power of groundwater level change alone for nitrate (R² = 0.04) and fluoride (R² = 0.04). However, controlled nexus model incorporating EC and fluoride explain up to 98.5% of nitrate variability and 77.7% of fluoride variability. Results reveal strong hydrogeochemical mediation of groundwater quality and demonstrate that fluoride behaves as a geogenically controlled parameter rather than a direct function of groundwater stress. The findings highlight the limitations of single-variable groundwater indicators and emphasize the necessity of nexus-based, multivariate approaches for groundwater quality assessment and management.