Vol. 14, Issue 1 (2026)

Groundwater is the primary source of drinking water in large parts of rural eastern India, yet its quality is increasingly threatened by both geogenic and anthropogenic factors. The present study evaluates the hydrochemical characteristics and drinking water suitability of groundwater sources in Madhepura district, Bihar, located in the Indo-Gangetic alluvial plain. A total of 50 groundwater samples collected from hand pumps and tube wells were analyzed for major physico-chemical parameters following standard analytical procedures. Hydrochemical facies were identified using Piper trilinear diagrams, while Gibbs plots were employed to understand the dominant processes controlling groundwater chemistry. The suitability of groundwater for human consumption was assessed using the Weighted Arithmetic Water Quality Index (WQI). Results indicate that groundwater is predominantly neutral to slightly alkaline and varies from moderately mineralized to highly mineralized. Piper diagram analysis reveals dominance of Ca-Mg-HCO? and mixed Ca-Mg-Cl water types, suggesting significant influence of carbonate weathering, ion exchange, and mixing processes. Gibbs plots indicate that rock-water interaction is the primary mechanism controlling groundwater chemistry, with secondary influence of evaporation. WQI values show that while a considerable proportion of samples fall under excellent to good categories, a substantial number are classified as poor to very poor due to elevated concentrations of total dissolved solids, hardness, nitrate, and fluoride. Spatial analysis using an interpolated WQI surface map highlights localized zones of degraded groundwater quality associated with intensive agricultural activity and shallow aquifers. The study underscores the need for regular groundwater quality monitoring, appropriate treatment measures, and sustainable management strategies to ensure safe drinking water supply in Madhepura district and similar alluvial regions.