Cost survey for Brazilian residential rainwater harvesting systems

Residential rainwater harvesting (RWH) systems usually have long paybacks and high initial outlays. Studies determining these costs often adopt different conventions, leading to varying results. This study presents a comprehensive cost survey for installing and operating typical residential RWH systems in eight cities in Brazil. The study simulated 432 RWH system design scenarios and two rainwater distribution schemes: indirect (with upper and lower rainwater tanks) and direct (with pressuriser). Initial outlays presented a 24% coefficient of variation among all systems. On average, direct rainwater distribution systems presented initial costs 1.4% lower than indirect systems. In such cases, higher costs corresponding to the pressuriser are equivalent to the savings obtained for not using an upper rainwater tank. Average initial costs for indirect systems ranged from R$ 10,999 to R$ 18,061, depending on the catchment area and rainwater tank size. Operational costs varied by 40% among all scenarios. Such variation is mainly due to the different potable water tariff schemes practised in each city. On average, systems with indirect rainwater distribution presented operational costs 1.8% lower than systems with direct rainwater distribution. As the main conclusion, the cost analysis indicates significant variation in installation and operational costs for RWH systems, pointing to the tariff scheme as a relevant factor for the economic viability of such systems.