Impact of pH, TDS, Chloride, and Nitrate on the Groundwater Quality Using Entropy-Weighted Water Quality Index and Statistical Analysis: A Case Study in the Districts of North India

Groundwater is a crucial asset to a healthy environment and public health. Various industrial practices, including improper disposal, inadequate waste management, and natural activities, serve as sources of groundwater contamination, further intensified by residential contributions, such as poor sanitation and sewage discharge. This study explores the groundwater quality status across a large geographical area of twenty-one districts in northern India by analyzing the spatial distribution of the key parameters- pH, total dissolved solids (TDS), chloride (Cl−), and nitrate (NO3−)- in 305 groundwater samples to identify the areas of concern that fall outside the safe consumption zone. Various physicochemical analyses, statistical analyses, i.e., normality test and hierarchical cluster analysis (HCA), and entropy-weighted water quality index (EWQI), were employed to assess groundwater quality throughout the research region. The results indicated 94% of samples were within the permissible pH range of 6.5–8.5. However, 6% of the samples exceeded permissible chloride values, and 9% fell beyond the TDS permissible limit, particularly in the southwestern regions of the study area. Notably, nitrate concentrations were observed within the permissible limits across the study area. The entropy weights were ordered based on the impact of the parameters as nitrate (0.408) > chloride (0.394) > TDS (0.196) > pH (0.002). In southwestern regions of the study area, the EWQI findings observed a deteriorated groundwater quality unsuitable for domestic usage. The HCA investigation classified the monitoring sites into two main clusters, cluster 1 showing low pollution and cluster 2 showing high pollution, which included 17% of the samples with high TDS and chloride concentrations. This highlights the contamination caused by human-induced activities and emphasizes the requirement for targeted groundwater management strategies to prevent further contamination and ensure the future suitability of groundwater quality.