Comprehensive evaluation of the possible impact of roofing materials on the quality of harvested rainwater for human consumption

Water is a vital natural resource that influences life and contributes to domestic and industrial activities. Availability and accessibility of safe water sources are crucial for a country's economic growth. Harvesting of roof runoffs is an alternative source of water used for domestic purposes. However, the quality of harvested rainwater can be affected by roofing materials. This research seeks to assess heavy metals concentration, physicochemical and bacteriological parameters in roof runoffs and estimate the water quality index and health risk these metals pose to consumers. Rainwater samples were collected from Aluzinc, Aluminum, Galvanized, and Asbestos roofing materials within the Ejisu municipality. Rainwater collected directly from the sky was used as control. All runoffs from the four roofing materials recorded Cd, Fe, Cr, turbidity, pH, E.coli, total and fecal coliform levels above WHO limit for drinking water. There was a significant variation in pH, EC, Zn, Cd, Cr, Fe, E. coli, total and fecal coliform levels between control samples and roof runoffs (p < 0.05). The estimated water quality index for runoffs from the four roofing materials exceeded 100 indicating their unsuitability for drinking. Cadmium recorded the highest non-cancer health risk to children and adults in all the roof runoffs. Hazard quotients (HQs) above one were recorded for a child (HQ = 40.1) and an adult (HQ = 13.6) via dermal exposure to Cd in runoff from Aluminum roofing material. Hazard quotient of 9.53 and 4.08 were estimated for a child and an adult respectively via oral exposure to Cd in runoffs from Asbestos roofing material. The estimated cancer risks were above 10⁻³ for a child and an adult via oral and dermal exposure to Cd in all roof runoffs, suggesting a possible cancer health effect. The study concludes that the four roofing materials impact negatively on the quality of runoffs.