Technical-financial evaluation of rainwater harvesting systems in commercial buildings-case ase studies from Sonae Sierra in Portugal and Brazil.

Water is an essential and increasingly scarce resource that should be preserved. The evolution of the human population and communities has contributed to the global decrease of potable water availability and the reduction of its consumption is now compulsory. Rainwater harvesting systems (RWHS) are emerging as a viable alternative source for water consumption in non-potable uses. The present study aims to contribute to the promotion of water efficiency, focusing on the application of rainwater harvesting systems in commercial buildings, and comprises four stages: (i) development of a technical evaluation tool to aid the design of RWHS and support their financial evaluation; (ii) validation of the tool using operational data from an existing RWHS installed at Colombo Shopping Center, in Lisbon, Portugal; (iii) assessment of the sensibility of the technical evaluation tool results to the variation of the inputs, namely the precipitation and consumption, through a parametric analysis for the Colombo Shopping Center; and (iv) comparison of the performance and financial feasibility of hypothetical RWHS in two existing commercial buildings. The technical tool was applied to two Sonae Sierra's shopping centers, one in Portugal and one in Brazil. The installation of a 200-m3 tank is advised for the first case study, allowing non-potable water savings of 60% but a payback period of about 19 years. In the Brazilian shopping, the implementation of a tank with a capacity ranging from 100 to 400 m3 leads to non-potable savings between 20 and 50%, but with smaller payback period, under 2 years, due to the relatively lower investment costs and higher water fees.

Financial feasibility of end-user designed rainwater harvesting and greywater reuse systems for high water use households.

Water availability pressures, competing end-uses and sewers at capacity are all drivers for change in urban water management. Rainwater harvesting (RWH) and greywater reuse (GWR) systems constitute alternatives to reduce drinking water usage and in the case of RWH, reduce roof runoff entering sewers. Despite the increasing popularity of installations in commercial buildings, RWH and GWR technologies at a household scale have proved less popular, across a range of global contexts. For systems designed from the top-down, this is often due to the lack of a favourable cost-benefit (where subsidies are unavailable), though few studies have focused on performing full capital and operational financial assessments, particularly in high water consumption households. Using a bottom-up design approach, based on a questionnaire survey with 35 households in a residential complex in Bucaramanga, Colombia, this article considers the initial financial feasibility of three RWH and GWR system configurations proposed for high water using households (equivalent to >203 L per capita per day). A full capital and operational financial assessment was performed at a more detailed level for the most viable design using historic rainfall data. For the selected configuration ('Alt 2'), the estimated potable water saving was 44% (equivalent to 131 m3/year) with a rate of return on investment of 6.5% and an estimated payback period of 23 years. As an initial end-user-driven design exercise, these results are promising and constitute a starting point for facilitating such approaches to urban water management at the household scale.