Performance Evaluation of Rainwater Harvesting on the Rooftops of Residential Buildings to Enhance Non-potable Water Demand in the Coastal Cities of Iran

Due to potable water shortage، groundwater pollution and an increase in water demand as a result of population growth، many Iranian communities، especially the coastal cities، are facing water crisis. Rainwater collection from the rooftops of residential buildings in towns and villages for non-potable water and greenery irrigation demand would be a practical solution to reduce the growing crisis of water supply for citizens. As the wide examples of ​impervious surfaces of cities are formed by the rooftops، the volume of rainwater harvested from the area is significant، which could be considered as a valuable alternative in water resources management. The rooftop rainwater harvesting system and the water tanks’ performance for storage and enhancement of daily non-potable water demand were analyzed in residential buildings in four coastal cities، namely Rasht، Gorgan، Bushehr and Bandar Abbas. Results of this study showed that if the tanks’ volume and daily non-potable water demand of residents calculated based on the physical and hydrological conditions of buildings، then rainwater storage in them would reach its maximum and the water demand. Large and small tanks could supply satisfied for a longer time. At least 75% of the non-potable water demand in 70 and 50 percent of the year، respectively in the City of Rasht. This will be 39% and 32% for the City of Gorgan، 15% and 11% for the City of Busher، and 10% and 7% for the City of Bandar Abbas.