Integrated assessment of drinking-water quality, health risk, and spatial patterns in a high-altitude Himalayan...

Safe drinking water remains difficult to secure in remote, high-altitude areas where communities depend largely on untreated natural sources and routine monitoring network is limited. This study evaluated whether source-level evidence that apparently acceptable bulk hydrochemistry can coexist with microbial and trace-metal health risks in Gilgit-Baltistan (GB), Pakistan. Eighty-six (86) drinking-water samples were collected during June-August 2024 from springs, snowmelt runoff, groundwater, and river/lake sources across six districts of GB. Physicochemical variables, trace metals, and total coliforms were evaluated using WHO and Pakistan standards, weighted arithmetic WQI, pollution indices, age-specific HHRA, multivariate statistics, and GIS-based hotspot mapping. Most samples were classified as excellent-good by WQI; however, poor-unsuitable categories occurred in localized hotspots, particularly where turbidity, Al, Fe, and As were elevated. Total coliforms exceeded the zero-tolerance guideline in 72.1% of samples, indicating widespread sanitary vulnerability that was not captured by WQI alone. Non-carcinogenic health risk exceeded the acceptable threshold (HI > 1) in 22.1% of adult and 30.2% of child exposure scenarios, with arsenic (As) and aluminum (Al) dominating risk. Total carcinogenic risk was controlled mainly by total Cr, As, and Pb. Because Cr speciation was not measured, Cr-related risk is interpreted as a conservative upper-bound screening estimate. Multivariate results indicated a regional mineralization gradient related to water-rock interaction, with localized trace-metal enrichment and microbial contamination reflecting source-specific geogenic and surface-contamination pathways. The findings show that integrated assessment is most useful when WQI is interpreted with contaminant-specific risk metrics and spatial evidence. This work provides a seasonal, source-level basis for prioritizing monitoring, source protection and point-of-use treatment in high-altitude communities.