Comprehensive assessment of physicochemical and microbial contamination and quantitative health risk of rainwater harvested from traditional thatched roofs in rural South Africa.

Abstract

Rooftop-rainwater harvesting is increasingly recognized as an alternative water supply that can reduce dependence on centralized water systems. This study evaluated the quality and health risks of rainwater harvested from thatched rooftops, a common roofing type in rural African communities. A total of 75 samples were collected from six rainfall events between October 2020 and December 2021 and analyzed for physicochemical parameters and microbial indicators. Most physicochemical parameters and trace metal concentrations complied with South African National Standards (SANS) and World Health Organization (WHO) drinking-water guidelines. Zinc was the most abundant metal, with concentrations ranging from 26.12 to 154.56 µg L-1. Arsenic exceeded guideline values only in first-flush samples from Tshikudini. Non-carcinogenic health risk assessment indicated negligible risks for most metals, although arsenic slightly exceeded the acceptable hazard quotient threshold for children in Tshikudini. In contrast, microbial contamination was widespread. Escherichia coli concentrations ranged from 13.3 to 104 cfu 100 mL-1, and both E. coli and total coliform counts exceeded recommended limits. Quantitative microbial risk assessment revealed a high probability of infection and illness, reaching 100% in most cases. Although harvested rainwater may be suitable for certain domestic uses, treatment is required before consumption to ensure public health protection.