Heavy metal pollution and hydrochemistry analysis of groundwater in Kathmandu Valley of Nepal and its health implications

The study conducted in Kathmandu Valley assessed water quality analyzing 50 water samples for hydrochemical parameters and heavy metals, employing rigorous quality control, data analysis with Origin software and ArcGIS, and various indices including Water Quality Index (WQI), Heavy Metals Pollution Index (HPI), Heavy Metal Evaluation Index (HEI), and Environmental Water Quality Index (EWQI), with human health risks from heavy metal exposure through Chronic Daily Intake (CDI) and Hazard Quotients (HQ). Piper diagram signifies, most of the selective falls under Ca²⁺-Mg²⁺-HCO₃ˉ composition indicates the temporary hardness. The heavy metal parameters follow the sequences of Fe > Mn > Zn > As > Cr > Ni > Pb > Cu > Cd with the mean value below the National Drinking Water Quality Standards except for Fe and Mn, and substantially heterogeneous spatial distribution patterns with 60 % samples as high metal class. The WQI categorizes high levels of Mn, NH₄⁺, Fe, and Pb, while assigning lower weights to Cu and Cd based on standard values and relative weights. The WQI value shows a high significant positive correlation with other indices, while the HPI values exceeding 100 in all samples indicate that the water is unsafe for drinking. Furthermore, the study depicts non-carcinogenic health risks from heavy metal exposure beyond acceptable levels across all sites, emphasizing the need for stronger regulation and enforcement with the development of remedial strategies and rigorous health risk assessment to improve the quality and public health concerns in the studied valley and in similar regions.