Drinking water quality & health risk assessment of secondary water supply systems in residential neighborhoods

Secondary water supply systems (SWSSs) are important components of the water supply infrastructure that ensure residents’ drinking water safety. SWSSs are characterized by long detention time, warm temperature, and unreasonable management, which may trigger the deterioration of water quality and increase risks. In this study, drinking water quality index (DWQI) and health risk assessment (HRA) were selected and modified to quantitatively assess the water quality and health risks of SWSSs in residential neighborhoods. In total, 121 seasonal water samples were selected. It was observed that the water quality was excellent with the DWQI of 0.14 ± 0.04, excluding one sample, which was extremely poor owing to its excessive total bacterial count. The HRA results revealed that the health risks were low: negligible non-carcinogenic risk for any population; negligible and acceptable carcinogenic risk for children aged 6–17 and adults. However, samples revealed higher carcinogenic risk (7.63 × 10⁻⁵ ± 3.29 × 10⁻⁶) for children aged 0–5, and arsenic was the major substance. Summer samples had poor water quality and higher health risks, which called for attention. To further investigate the water quality and health risks of SWSSs, monthly sampling was conducted during summer. All 24 water samples were qualified in Chinese standard (Gb 5749-2022) and characterized as excellent quality. Their HRA results were consistent with the seasonal samples’ and the health risks were mainly concentrated in May. Overall, our study provides a suitable framework for water quality security, advice for managers, and references for administrators in other cities.