Water quality assessment of rooftop harvested rainwater across different roof types in a semi-arid region of South Africa.

Abstract

Uneven distribution of precipitation and climate change have led to water shortages, adversely impacting numerous countries worldwide. Rooftop rainwater harvesting (RWH) has emerged as a crucial method for providing water for domestic uses. However, there are concerns about the quality of rainwater collected from roofs, as it may be contaminated with pollutants such as metals and microbiological pathogens. This study investigates the common roof types used as catchments for rainwater harvesting with the aim of establishing the quality and usefulness of the harvested water resource. Compliant levels of major and trace metals were recorded across various roof types in the three study areas. Metals of concern, such as lead (below detection limit to 0.69 μg/l), arsenic (0.06-0.13 μg/l), and cadmium (0.02-0.13 μg/l), were also within acceptable limits at all study sites. However, the average levels of E. coli detected ranged from 4.32 to 27.97 cfu/100 ml, exceeding the recommended limits set by both the World Health Organization and the South African National Standards. The trace metal levels in water collected from slate roofs were slightly higher than those from other roof types for most of the metals studied. The quality of the water obtained from various roof types indicates it is suitable for all domestic purposes, including drinking after disinfection. No significant differences were observed in the water quality across the different rooftops in the study areas. PRACTITIONER POINTS: Different roofing materials did not significantly affect the quality of the harvested rainwater. Water quality of the harvested rainwater complied with regulatory standards except for microbial water quality parameters. Rainwater can be used for several domestic purposes without treatment except for drinking purposes where it should be treated with a simple point-of-use water treatment system. First flush should be discarded as it impacts greatly on the water quality parameters determined. Rainwater harvesting offers an alternative and supplementary form of water supply in the semi-arid region of South Africa.