Potential of rooftop rainwater harvesting to meet outdoor water demand in arid regions

The feasibility of rooftop rainwater harvesting (RRWH) as an alternative source of water to meet the outdoor water demand in nine states of the U.S. was evaluated using a system dynamics model developed in Systems Thinking, Experimental Learning Laboratory with Animation. The state of Arizona was selected to evaluate the effects of the selected model parameters on the efficacy of RRWH since among the nine states the arid region of Arizona showed the least potential of meeting the outdoor water demand with rain harvested water. The analyses were conducted on a monthly basis across a 10-year projected period from 2015 to 2024. The results showed that RRWH as a potential source of water was highly sensitive to certain model parameters such as the outdoor water demand, the use of desert landscaping, and the percentage of existing houses with RRWH. A significant difference (as high as 37.5%) in rainwater potential was observed between the projected wet and dry climate conditions in Arizona. The analysis of the dynamics of the storage tanks suggested that a 1.0–2.0 m3 rainwater barrel, on an average, can store approximately 80% of the monthly rainwater generated from the rooftops in Arizona, even across the high seasonal variation. This interactive model can be used as a quick estimator of the amount of water that could be generated, stored, and utilized through RRWH systems in the U.S. under different climate conditions. The findings of such comprehensive analyses may help regional policymakers, especially in arid regions, to develop a sustainable water management infrastructure.