Assessing tradeoffs of strategies for urban water conservation and fit for purpose water

Improved understanding of the effects of strategies that reduce demand for traditional water supplies (i.e. conservation and reuse) is important to foster the transition toward resilient municipal water supply systems. This study assesses water demand and cost tradeoffs among strategies in three U.S. cities; Denver, CO; Miami, FL; and Tucson, AZ. A comprehensive set of strategies to reduce demand for traditional supplies were evaluated individually and in combination, including: indoor conservation fixtures, irrigation efficiency, climate appropriate landscape, and use of alternate water sources (i.e. graywater, wastewater, stormwater, and roof runoff). The Integrated Urban Water Model (IUWM) is reconciled with the NSGA II multiobjective optimization approach to explore tradeoffs and to identify optimal solutions. Results demonstrate differences in the set of optimal water demand reduction strategies across the three study cities due to unique differences in climate, land development patterns, and water use behaviors. 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 offer benefits for achieving a balance between cost and demand for traditional supplies.