Assessing Regional Tradeoffs for Fit-for-Purpose Water and End-Use Efficiency

As water utilities transition toward water supply resiliency, fit-for-purpose water systems (i.e., use of alternate water supplies) and end use efficiency are increasingly considered for water demand management. This study assesses tradeoffs between cost and demand reduction potential in three U.S. cities; Denver, CO; Miami, FL; and Tucson, AZ. These cities were selected due their diverse climate and urban development patterns. A comprehensive set of water demand reduction strategies were evaluated: indoor conservation fixtures, irrigation efficiency, xeriscape, and use of alternate water sources (graywater, wastewater, stormwater, and roof runoff). The Integrated Urban Water Model (IUWM) is coupled with the NSGA II multiobjective optimization approach to explore tradeoffs between cost and demand reduction potential, identifying optimal solutions. Results demonstrate differences in the set of optimal water demand reduction strategies across the three study cities. Efficient irrigation systems were highly effective across the study cities when considering cost and demand reduction tradeoffs. Stormwater use has large potential for demand reduction even in arid regions, but is a very costly strategy. When alternate water sources are considered, wastewater use for irrigation and graywater use for toilet flushing at the multi-residential scale can achieve a balance between cost and demand for traditional supplies.