<p>The study employs the second Parfait-Hounsinou method to evaluate the overall groundwater quality in the Thrissur corporation, southern India, using two alphabetical letters (e.g., BC) to denote the CWQI and MWQI, respectively. Data included pH, EC, TDS, TH, Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^–, SO₄²⁻, HCO₃⁻, NO₃⁻, total coliform, fecal coliform, and intestinal enterococci. The CWQI classifications revealed that all samples were chemically safe for human consumption, whereas the MWQI classifications indicated that the majority of samples were microbiologically unsafe. The second Parfait-Hounsinou method integrates both indicators to obtain an overall quality rating, which classifies the groundwater in the study area as unsuitable for human use. The graphical representation of the method facilitates the identification of the dominant chemical parameters and their compliance with WHO standards. The isotopic composition (δ²H and δ¹⁸O) and hydrogeochemical signatures of groundwater indicate a meteoric origin with minimal evaporative influence, where positive deuterium excess and dominant Na⁺–Cl⁻ chemistry highlighting the role of source moisture variability and rock–water interactions in controlling groundwater quality. The study concludes that the second Parfait-Hounsinou method is more effective than traditional WQI for evaluating water quality and highlights the need for proper groundwater management, as good soil drainage and high rainfall are insufficient for sustainability.</p>