Rainwater Reuse in Urban Areas: A Mathematical Model and a Long-Term Modelling Approach

Natural water resources are becoming increasingly limited due to global-scale climate change and water availability issues have become so severe that they must be addressed. Given these issues, reuse of wastewater and rainwater provides a promising way to cope with water shortages. This paper describes an investigation into the efficiency of rainwater usage systems. A conceptual model was built to assess the behaviour of rainwater tanks and their effectiveness in coping with water shortages. The study is based on a longterm simulation (12 years) of different rainwater reuse tank schemes. The associated reductions in residential freshwater demand (water reuse efficiency) and wet-weather runoff delivered to the sewer system (sewer discharge efficiency) were surveyed. The results clearly show that rainwater usage systems can significantly reduce drinking water consumption. The specific volumes required for the reuse of rainwater are high; however, for local scale application, the specific volumes necessary are comparable to the reservoir volumes already used to store freshwater resources during potable water shortage.