Assessing water quality and potential human health risks of drinking water sources based on an integrated-weight water quality index: a case study of the Daotian River basin, Southwest China

In the karst regions of Southwest China, groundwater commonly discharges to the surface as springs, which serve as a primary drinking water source for local residents. Accordingly, assessing spring water quality and associated human health risks in karst watersheds is critical to sustainable regional economic development. This study investigated the water source area of the Daotian River in Bijie, Guizhou Province, based on 48 collected spring water samples (comprising 30 from dolomite springs, seven from limestone springs, and 11 from non-karst springs). Hydrochemical parameters derived from field surveys and laboratory analyses were used to identify groundwater hydrochemical facies and determine their underlying controlling factors. Water quality and non-carcinogenic human health risks via oral ingestion were assessed using the integrated-weight water quality index (IWQI) and a human health risk assessment (HHRA) model. The results indicate that the dolomite springs are predominantly of the HCO₃–Ca·Mg and HCO₃·SO₄–Ca·Mg types, the limestone springs exclusively exhibit a hydrochemical type of HCO₃–Ca, while the non-karst springs are primarily of the HCO₃–Ca and HCO₃·SO₄–Ca·Mg types. Rock weathering and agricultural activities serve as the dominant factors governing the groundwater geochemistry across the river basin. The water quality assessment indicates that the spring water samples exhibited IWQI values ranging from 16.02 to 100.91, with those of excellent, good, medium, and poor water quality accounting for 14.58%, 60.42%, 20.83%, and 4.17% of the total samples, respectively. The water quality assessment reveals that the hazard index (HI) values of the spring water samples varied from 0.06 to 3.08. Among the assessed hydrochemical constituents, NO₃⁻ and Cr contributed the most significantly to the HI, accounting for 70.39% and 13.99% of the total risk, respectively. Monte Carlo simulations further indicate that the ingestion rate (IR) and average exposure time (AT) exerted a substantial influence on the resulting HI values. The spatial patterns of the HI for the four target demographic groups (infants, children, adult females, and adult males) align with the spatial distribution of the IWQI values of the river basin, with high-value zones of both metrics concentrated in the lower reaches near the river basin outlet. From the perspective of oral ingestion, springs in the middle and lower reaches of the river basin impose significantly higher potential non-carcinogenic health risks to infants compared to other demographic groups, while the vast majority of springs pose low health risks to adults and children. The results of this study provide a scientific framework to support policymakers in formulating sustainable strategies for water resource management in small karst watersheds.