Water is a critical ecosystem service, whose scarcity is increasing in urban and peri-urban areas commensurate with population growth. This paper reports on the potential of roof-based rainwater harvesting as an option in mitigating this challenge and complementing metered water supplies. Roof footprints were mapped and computed using standard GIS procedures. A social survey using questionnaires was used to collect data from homeowners in the estate. The social data were subjected to descriptive statistics to yield general trends on water availability, use, and management. Rainfall data covering the period 2005-2017 was obtained from the Kenyatta University Field Meteorological Station. Results showed that at least 90% of households depend on Nairobi Water and Sewerage Company for water. Despite the prevailing water shortages, about 80% of homes lack complete and functioning rainwater harvesting infrastructure. Potential harvests based on a standard roof area of 350 m 2 per residence range from 5250 to 63,350 litres per month, with a mean of 26,000 litres. The two rainy seasons can in particular yield significant quantities of water and greatly enhance water security in the area. Scaling-up of rainwater harvesting can however benefit from appropriate policy incentives such as lowering the cost of plastic tanks to make them more affordable, and including rainwater harvesting infrastructure as a requirement for construction approvals.