Evaluation of Rainwater Harvesting Systems Installed in Residential Buildings in Ogun State

Rainwater harvesting offers a sustainable water supply alternative for residential buildings in Ogun State, South West Nigeria, where potable water supply is inconsistent. This study evaluated the design adequacy, material quality, and functional performance of rainwater harvesting systems installed in residential buildings in Ijebu-Ode, Sagamu, and Abeokuta Local Government Areas of Ogun State. A field survey of 60 residential properties with rainwater harvesting systems was conducted, combining physical inspection of system components (roof catchment, guttering, first-flush diverters, storage tanks, and filtration) with water quality testing and household user interviews. Design adequacy was assessed against BS EN 16941-1:2018 guidelines. Water quality parameters tested included turbidity, pH, total coliform count, and nitrates. Results showed that 78% of systems had inadequate first-flush diverter provision, leading to elevated turbidity in stored water. Total coliform contamination was detected in 63% of sampled tank water, with E. coli present in 22% of samples, indicating significant microbiological risk. Storage tank sizing was inadequate (below recommended capacity) in 44% of systems. User satisfaction was high (mean: 3.9 out of 5) despite the documented deficiencies, suggesting low awareness of water safety standards among homeowners. Recommendations include mandatory rainwater harvesting system inspection as part of building occupancy certification in Ogun State, and public education on system maintenance and water safety.

Keywords: rainwater harvesting, residential buildings, water quality, Ogun State, sustainable water supply