Groundwater quality, human health risks and major driving factors in arid and semi-arid regions of Rajasthan, India

Evaluating status, variability and identifying the factors influencing groundwater quality is essential to manage and conserve groundwater resources. The present study aims to examine groundwater quality for 15 water quality parameters from 84 stations in arid and semi-arid districts of Rajasthan, India, using annual data from 2000 to 2018. Statistical methods such as descriptive test statistics, Mann-Kendall (MK) test, Sen's slope estimation, and Principal component analysis (PCA) were used to analyze the hydrochemical parameters. While World Health Organisation (WHO) and Bureau of Indian Standards (BIS) guidelines were used to assess the suitability of groundwater for domestic purposes, sodium adsorption ratio (SAR), electrical conductivity (EC), and United States Salinity (USSL) diagrams were used for irrigation suitability. Further Generalized Additive Model (GAM) was used to explore the effect of climatic (precipitation, temperature) and anthropogenic (net irrigated area (NIA), fertilizer usage, industrialization, and population) variables on groundwater quality. The empirical results reveal that in groundwater of the study area sodium (Na+) and potassium (K+) were the dominating cations, while chloride (Cl−) and bicarbonate (HCO3−) were the dominating anions. The groundwater was predominantly Na–Cl type. Further, most stations witnessed an increasing trend in calcium, magnesium, sodium, chloride, bicarbonate and sulphate and a decreasing trend in potassium, fluoride and nitrate. The SAR, EC, and USSL indicate that the groundwater in the region is suitable for irrigation if salinity control measures are implemented. Chloride, fluoride and sodium concentrations exceeded the prescribed guideline limits in most stations, jeopardizing the suitability of water for drinking and posing significant health hazards. The GAM analysis revealed that anthropogenic variables significantly impact the groundwater quality parameters compared to the climatic variables. Accordingly, it is suggested that anthropogenic parameters must be addressed while formulating groundwater resource management policies. Thus, policies should focus on the stringent enactment of regulations and guidelines controlling the excessive use of fertilizers, implementing proper disposal of municipal solid and liquid waste, and managing industrial pollutants.