Residential rainwater harvesting: Effects of incentive policies and water consumption over economic feasibility

- Water demand is the key variable for economic feasibility in a structured water tariff system.
- A higher percentage of rainwater use does not necessarily improve economic gains from the user's point of view, and this depends on the water tariff structure and household monthly water consumption.
- Government subsidies on initial costs improve economic feasibility in most cases, but certain users will not obtain benefits even when installation costs are low.

Rainwater harvesting is currently a recurring theme as part of the sustainable practices for urban constructions. The economic feasibility of implementing a system capable of capturing, treating and distributing rainwater for residential uses concerns the user who intends to benefit from such practice. To this end, twelve single-family houses of different construction standards were selected for this research in the city of Belém, Pará, Brazil. The design and budget for the installation of a rainwater harvesting system were prepared for each house. The hydrological performance and economic feasibility were evaluated under different consumption and economic policies scenarios using the rainwater harvesting simulation software. The main conclusion is that rainwater systems are more economically feasible in households with higher water demand, regardless of the size of the catchment area. The cost of implementing rainwater systems has little variation with the construction standard of the residence where it is installed. The tariff structure makes it economically unfeasible to harvest rainwater in any scenario for houses where water consumption is below the social tariff or receives fixed price water bill. A combination of rising water prices to the same level of water production costs and reduced implementation costs improves the economic feasibility of rainwater harvesting.