Rainwater harvesting to irrigate small-scale gardens enhances food self-sufficiency to overcome rural poverty. So far rainwater harvesting is not encouraged by the Namibian National Water Supply and Sanitation Policy nor supported financially by the Namibian government. This study proposes two rainwater harvesting facilities to irrigate gardens; one collects rain from household roofs with tank storage, the second collects rain on a pond roof with pond storage. The aim of this paper is to assess the benefits of rainwater harvesting-based gardening and to propose policy and financing implications for the Namibian government. We investigate the benefits of rainwater harvesting through a literature review, a cost–benefit analysis, monitoring of project pilot plants and a comparison with the existing irrigation and drinking water infrastructure. The results indicate that rainwater harvesting offers numerous benefits in technological, economic, environmental and social terms. The facilities have a positive net present value under favourable circumstances. However, material investment costs pose a financing problem. We recommend that government fund the rainwater harvesting infrastructure and finance privately garden and operation and maintenance costs. Integrating these aspects into a national rainwater harvesting policy would create the conditions to achieve the benefits of an up-scale of rainwater harvesting based gardening in Namibia.