At a building or dwelling scale, accurate evaluation of the water savings potential from rainwater harvesting (RWH) can be achieved by simulating the performance of the RWH system using a balance equations model. At an urban scale, water savings potential is usually estimated from the balance between the annual rainfall and annual water consumption. This approach has limited accuracy since it assumes an infinite storage capacity and it disregards the variability of the ratio between the water collected and water consumed in each building. This paper presents a methodology to evaluate rainwater harvesting potential at an urban level taking into consideration buildings' characteristics and consumption pattern. The complexity of the model is balanced with the format and detail of the information available to allow fast and easy implementation with few resources. The proposed methodology is applied to the city of Lisbon, Portugal, located on the Atlantic coast of the Mediterranean climate region. The results demonstrate water savings potential ranging from 16 to 86% depending on the buildings and occupancy characteristics. The spatial variability of the rainfall in the city of Lisbon was found to be negligible for rainwater harvesting potential evaluation.
Keywords: Accuracy/data requirements balance; Parametric water savings potential functions; Rainwater harvesting systems simulation; Urban planning; Water savings potential.