Financial feasibility and environmental analysis of potential rainwater harvesting systems: A case study in Spain

Abstract

Spain has one of the highest risks of water shortage due mainly to the growth of the urban population, the development of different economic activities, such as tourism, in regions with major hydrological constraints and under the effect of global climate change. Government authorities and public and private institutions have stressed the need to develop alternative water supplies to respond to the growing demand in cities, which are home to more than 70% of Spain's population. Rainwater constitutes an alternative water supply for uses that require lower quality than that provided by tap water. Although there are financial-feasibility studies and other studies on the potential environmental impacts of Rainwater Harvesting (RWH) systems, there is no integration between these studies that allows for rapid assessment tools for these systems that can be used by planners and decision makers. This study shows that it is possible to model both conventional financial indicators (Net Present Value and Internal Rate of Return) and indicators of potential environmental impact (Global Warming Potential and Energy Use) using linear systems and an appropriate sizing scale for the majority of RWH systems. Some positive financial results of this study indicate negative environmental performance in some configurations of RWH systems. In addition, providing rainwater to meet domestic water demand for washing machines has a lower impact than using tap water. The determining factor in the design of RWH systems is the scale of the system, where the neighbourhood scale is the best alternative. The material used for storage tanks is not an outstanding factor.