Rainwater Reuse Project (RRP): Rainwater Treatment to removeAtmospheric Pollutants and Assessment of Impact on Population Health

This paper presents the scientific findings and societal impacts of the Rainwater Reuse Project (RRP), a one-year investigation of roof-harvested rainwater (RHRW) quality and associated health risks in Ikorodu, Nigeria. A total of 120 rainwater samples were collected monthly from free-fall rainfall, rooftop runoff, and storage tanks during wet and dry seasons. Atmospheric particulate deposition was measured using passive deposition collectors, while microbial contamination was assessed using standard culture-based assays for total coliforms, Escherichia coli, and heterotrophic bacteria. Mean particulate deposition rates ranged from 15.2 to 27.6 mg m⁻² day⁻¹, with higher loads recorded during the dry season. Average total coliform and E. coli concentrations in untreated RHRW were 2.4 × 10³ MPN/100 mL and 1.8 × 10² MPN/100 mL, respectively. First-flush diversion reduced microbial contamination by 35–60%, depending on roof material. Household water treatment techniques (HWTTs) were also evaluated. Boiling, chlorination, alum treatment, and combined alum–chlorination treatment achieved mean bacterial reductions of 99.9%, 99.3%, 38.4%, and 99.9%, respectively. Quantitative Microbial Risk Assessment (QMRA) indicated that untreated RHRW posed a significant health risk, with estimated pathogen exposure risks of up to 100 infections per 10,000 exposed households annually, decreasing only slightly to 96 per 10,000 following alum treatment alone. In contrast, boiling and combined alum–chlorination treatment reduced infection risks to below 10⁻⁴ per person per year and achieved disability-adjusted life year (DALY) values within the WHO benchmark. Questionnaire surveys (n = 125 households) also indicated strong community acceptance of treated rainwater. The findings demonstrate that appropriately treated RHRW can provide a safe and sustainable source of potable and non-potable water in tropical and subtropical regions.