Assessment of Stormwater Harvesting Design Potential in Institutional Buildings in Ile-Ife, Osun State

Water scarcity is an increasingly acute challenge in Nigerian institutional settings, and stormwater harvesting from building roofscapes represents a technically viable and architecturally integrable water supplementation strategy that is underexplored in the Nigerian context. This study assesses the stormwater harvesting potential of institutional buildings at the Obafemi Awolowo University campus in Ile-Ife, Osun State, examining roof catchment areas, runoff coefficients, and rainfall data as the primary determinants of harvestable yield. Roof areas of fifteen representative buildings, including faculty blocks, student hostels, and administrative buildings, were measured from architectural drawings and verified by field survey. Monthly rainfall data for Ile-Ife from 2018 to 2023 from the Nigerian Meteorological Agency were analysed for seasonal variability and design rainfall parameters. Harvestable yield calculations were performed for each building using the mass balance method, accounting for evaporative losses and a water quality reduction factor. Demand analysis assessed the potential for harvested water to substitute for treated municipal supply in toilet flushing and landscape irrigation uses. Results indicate that the student hostel buildings, with their large unobstructed roof areas, offer the highest harvesting potential per building, collectively capable of supplying an estimated forty-two percent of their annual toilet flushing demand from harvested stormwater under average rainfall conditions. First flush diverter and cistern sizing recommendations are provided for five priority buildings. The study recommends a pilot stormwater harvesting installation at one student hostel as a demonstration project aligned with the OAU green campus sustainability initiative. Keywords: stormwater harvesting, institutional buildings, Obafemi Awolowo University, water conservation, sustainable architecture.