A Scenario-Driven Assessment of the Economic Feasibility of Rainwater Harvesting Using Optimized Storage

Abstract

Regional water scarcity has given rise to the search for sustainable means of water supply. Rainwater harvesting (RWH) has been receiving unprecedented attention as low-cost and eco-friendly option. Given the conflicting nature of research findings with respect to the feasibility of RWH and the belief that such results have sometimes been unreasonably generalized, this study was undertaken to ascertain the feasibility of RWH under very specific climatic and socio-economic conditions. This study investigated the economic feasibility of RWH in a sub-Saharan African city (Enugu, Nigeria), considering eight dwelling categories. Life cycle cost analysis was performed for RWH system in each of the categories for specified levels of water consumption namely: basic water need (50 litres per capita per day, lpcd), pour flush (75 lpcd) and full plumbing connection (150 lpcd) and for two energy options namely: fuel generator and the national power supply grid. Capital cost ranged from 47 to 95% of the net present value (NPV), maintenance cost ranged from 4 to 40% and running cost ranged from 1 to 27% of NPV. The percentage cost contribution of underground tank to NPV ranged from 60.4–82%, 66.9–86% and 77.3–89% for basic water need, pour flush and full plumbing connection options respectively, using the national electricity grid as source of power for pumping water to the overhead tank. The corresponding cost contributions for the use of petrol generator as source of power for pumping are 56.5–75.9%, 63–81% and 73.9–85%. The unit cost of water ranged from 0.07–0.25 N/litres, 0.09–0.34 N/litres and 0.22–0.54 N/litres for basic water need, pour flush and full plumbing connection, using the national grid for pumping water. The corresponding unit costs for generator are 0.09–0.3 N/litres, 0.11–0.4 N/litres and 0.28–0.64 N/litres. Comparison of these costs with the costs of other sources of water supply shows that RWH is a cheaper source of water. 1$ = N360.