Assessing sources of groundwater quality and health risks using graphical, multivariate, and index techniques from a part of Rajasthan, India

Groundwater provides sustainable potable water in developing countries like India. However, contaminated groundwater directly affects human health. The United Nation policy is to provide clean water for all by 2030. Therefore, groundwater samples collected from a part of Rajasthan, India were analysed for chemical parameters to identify the sources of groundwater quality variation and associated health risks. To achieve this objective, a comprehensive approach of entropy water quality index (EWQI), Piper and Gibbs diagrams, ionic ratios (IR), synthetic pollution index (SPI), principal component analysis (PCA), and non-carcinogenic health risk (NHR) methods were used. EWQI revealed that groundwater quality is not fit for drinking in 81.86% of the area due to higher TDS, Na⁺, ${\text{Cl}}^{-}$, ${\text{SO}}_4^{2-}$, ${\text{NO}}_3^{-}$, and $F^{-}$ contents, which was statistically significant by ANOVA test. Modified Piper's diagram identified Ca²⁺ - ${\text{HCO}}_3^{-}$, Ca²⁺ - ${\text{Cl}}^{-}$, Na⁺- ${\text{Cl}}^{-}$, and Na⁺ - ${\text{HCO}}_3^{-}$ types in 36.67%, 22.73%, 13.64%, and 27.27% of groundwater samples, respectively. Gibbs diagrams illustrated that 59.09% and 40.81% of groundwater samples fell in the rock and evaporation domains, respectively. IR demonstrated that geogenic processes (mineral dissolution, ion exchange, and evaporation) and anthropogenic activities cause groundwater quality degradation. PCA indicated that PC1 has high loadings of TDS, Mg²⁺, Na⁺, ${\text{Cl}}^{-}$, and ${\text{SO}}_4^{2-}$, PC2 shows high loadings of pH and $F^{-}$, and PC3 represents high loadings of ${\text{NO}}_3^{-}$, K⁺, and ${\text{HCO}}_3^{-}$, which was further supported by t-test analysis. SPI revealed that 99.82% of the study area is polluted. NHR values (0.03 to 1.68, 0.02 to 1.29, and 0.03 to 1.30 for children, women, and men, respectively) showed that long-term exposure to ${\text{NO}}_3^{-}$ and $F^{-}$-containing drinking water poses a higher health risk to children compared to men and women. Regular water quality monitoring, sanitation facilities, limited application of agrochemicals, etc. were suggested. Such a study would aid environmental public health programs.