Evaluation of Stormwater Harvesting Potential for Domestic Use in Semi-Arid Communities of Sokoto State

This study evaluates the technical and practical potential for rooftop stormwater harvesting as a supplementary domestic water supply in semi-arid rural communities of Sokoto State, North West Nigeria. Sokoto State receives an average annual rainfall of approximately 500 to 700 millimetres concentrated in a five-month wet season, and rural communities face acute water scarcity during the seven-month dry season when groundwater levels decline and surface water sources diminish. A field-based assessment was conducted in six rural communities in Tambuwal and Goronyo Local Government Areas to characterise rooftop catchment areas, estimate rainwater harvesting yields using measured rainfall data, assess household water demand, and evaluate water quality of harvested rainwater. Storage tank sizing calculations were performed for the average household using the critical period method. Results indicate that an average household with a 40-square-metre rooftop catchment and a 3,000-litre storage tank can meet approximately 40 percent of its basic water demand through the wet season and up to six weeks into the dry season under median rainfall conditions. Water quality analysis of harvested samples shows contamination from bird droppings and roof surface accumulation, requiring a simple first-flush diverter and chlorination to meet drinking water standards. Economic analysis demonstrates that a community-organised group tank procurement scheme can reduce capital cost per household to a level affordable for most rural families. Recommendations include integrating rooftop harvesting into the Sokoto State rural water supply programme. Keywords: rainwater harvesting, stormwater, semi-arid, water security, Sokoto State.