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-m 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 m 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.