Evaluation of rainwater harvesting system in university buildings for non-potable water demand

Urban water demand for potable water is significantly increasing due to population growth. Harvesting rainwater can reduce the pressure on the supply main and groundwater usage for non-potable water usage. In this study, the SWMM LID modelling framework was used to investigate the rainwater harvesting potential of 5 academic buildings on the university campus to compensate for daily non-potable water usage such as toilet flushing, lawn irrigation and car or bus washing. The water saving efficiency (WSE) of the RWH system for two different storage scenarios: (i) rain barrel only (50000 L), and (ii) rain barrel and underground (UG) water tank (140000) was estimated by simulating a hydraulic model using historical daily rainfall data (1982-2021). The results suggest that the WSE of non-potable water demand is greatly influenced by storage capacity, number of users, and area of usage. For toilet flushing, 29% WSE is obtained for 100 toilet users daily. WSE varies from 34.3 to 100% for irrigation depending on storage volume of 50,000 L and 140,000 L, respectively. Scenario 1 achieves 51.3-100% WSE for car and bus washing water demand for 10 buses and 10 cars, respectively. Scenario 2 fulfils the water demand for 28 cars or 14 buses. The results also showed that a cost savings of $23 for scenario 1 and $63.41 for scenario 2 could be achieved if $0.45 per 1000 L water price is considered with pumping cost, but a higher return can be achieved if drinking water requirement can be fulfilled with harvested rainwater.