Novel Insights into the Spatiotemporal Variation of Tap Water Quality and Disinfection Byproducts with Implications for Cancer Risk in Zhejiang, China

Ensuring safe drinking water is essential for public health. In this study, we sampled tap water from 10 regions of Zhejiang Province, China, and measured dissolved organic carbon (DOC), UV absorbance at 254 nm (UV₂₅₄), and six classes of disinfection byproducts (DBPs): trihalomethanes (THMs), iodinated THMs (I-THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), haloacetamides (HAMs), and haloketones (HKs). We found that northern Zhejiang had higher DOC and UV₂₅₄ levels, which reflected differences in source water type and elevation-driven land-use patterns. Consequently, THMs, ITHMs, HAAs, and HANs were more abundant in the north, particularly in winter. HAMs peaked in summer, while HKs showed no clear pattern. Although rainfall influenced bromide levels, bromine incorporation into DBPs was mainly driven by precursor properties rather than bromide concentration. Finally, regions with higher total cancer incidence rates (TCRs) had elevated concentrations of I-THMs, triHAAs, and other brominated DBPs. TCR was higher in areas with higher UV₂₅₄ and lower water source altitude. These findings suggest that (1) switching to higher-altitude water sources and (2) optimizing water treatment strategies to reduce UV₂₅₄ levels could help mitigate DBP-related health risks. This study highlights the need for region-specific water management and offers insights for improving water safety in similar contexts worldwide.