Rainwater harvesting (RWH) plays an important role in increasing water security for individuals and governments. The demand for tools to enable technical and economic analysis of RWH systems has led to a substantial body of research in the recent past. This paper focuses on the economic aspects of domestic RWH in urban and peri-urban environments. In this regard, key issues are identified and discussed including quality and quantity of harvested water, the water demand profile, the scale of installation, interest rates, the period of analysis, real estate value, and the water-energy-food nexus. Kenya and Australia are used as reference points having different economies and opposing RWH policies. It has been found that the previous studies on financial aspects of RWH systems often had conflicting results. Most of the economic analyses have ignored the full benefits that a RWH system can offer. In view of the varying and conflicting results, there is a need to standardize the methods of economic analysis of RWH systems.

Food and water are at the heart of sustainable development. Roof-harvested rainwater kept in rainwater storage systems (RSS) and used in household agriculture (HA) has the potential to increase yields and supplement household nutrition. Combined systems may contribute to at least eight of the United Nations’ 17 Sustainable Development Goals (SDGs). In this paper, a daily analysis tool, ERain, is used to assess what area of vegetables can be reliably irrigated by roof-harvested rainwater. A socio-economic context is built around an orphanage in the semi-humid region of Nakuru, Kenya. Comparisons are made with the semi-arid region of East Pokot. A 225 kL closed masonry tank and a 1 ML open reservoir with an additional 8 kL/day of recycled water entering are analyzed for various roof sizes. The 225 kL RSS connected to 1000 m² of roof and irrigating 1000 m² could increase yields from 1850 to 4200 kg/year in Nakuru. If evaporation was controlled, the 1 mL RSS and recycled water system could support 4000 m² of land, yielding nearly 20,000 kg/year, which is enough to meet the WHO recommended vegetable dietary requirements of the orphanage. A combination of crops, some for consumption and some for sale, could be grown.

The production and distribution of a sufficient quantity of food and water of satisfactory quality is at the heart of sustainable development. At the small domestic scale, roof-harvested rainwater can make a significant contribution to food supply and distribution systems (production, handling, storage, and transportation). In this paper, we compare the potential crop production of a small garden plot using three methods of watering: (1) rainfed only with no irrigation; (2) irrigated with the ideal amount of water; and (3) rainwater tanks of various sizes installed and used to irrigate the plot. Yield was determined on the basis of the yield calculation method presented in FAO 33. It was found that yields can be increased considerably by installing a correctly managed rainwater storage system (RSS). A 3 kL RSS connected to a 120 m² roof can increase yields in Nairobi from 40 kg to 96 kg. In Sydney, a larger roof of 200 m² can increase yields from 66 kg to 143 kg. This study makes an important contribution to water and food security-related sustainable development goals.