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Abstract Urban agriculture has significant potential to address food security and nutritional challenges in cities. However, water access for urban food production poses a major challenge in the face of climate change and growing global freshwater scarcity, particularly in arid and semi‐arid areas. To support sustainable urban food production, this study focuses on a hybrid urban water system that integrates two important alternative water resources: a decentralized system of rainwater harvesting (RWH) and a centralized reclaimed water system. A new spatial optimization model is developed to identify the best investment strategy for deploying these two alternative water infrastructures to expand urban food production. The model is applied to the case study in Tucson, Arizona, a semi‐arid city in U.S. Southwest, to address food deserts in the region. Results show that 72%–96% of the investment is allocated to rainwater tanks deployment across all investment scenarios, with the proportion of investment in rainwater harvesting increasing as total investment rises. However, rainwater contributes only about 18%–27% of the total food production. The results of our case study indicate that expanding the reclaimed water network is more effective for urban food production and is also more cost‐efficient compared to implementing rainwater tanks. The new model can be applied to other regions, taking into account factors such as crop types, climate, soil conditions, infrastructure configurations, costs, and other site‐specific variables. The study provides valuable insights for planning urban water systems that incorporate alternative water sources under different investment scenarios. 

Abstract Urban centers around the world are grappling with the challenges associated with population increases, drought, and projected water shortages. Potable water reuse (i.e., purification of municipal wastewater for reuse as drinking water) is an option for supplementing existing water supplies. Public perception research on potable water reuse has predominantly employed surveys with multiple‐choice questions that constrain survey respondents to describe their concerns by choosing from several response options. This research examines hundreds of write‐in responses to a large public survey in Albuquerque, New Mexico, to provide a detailed analysis of residents' questions and concerns about potable water reuse. Findings demonstrate that allowing respondents to voice their actual concerns adds richness and nuance that cannot be obtained from multiple‐choice response data alone. Especially with controversial resource considerations, such as potable water reuse, planners would benefit from a full understanding of the problem before engaging with the community. 

The Colorado River supplies >40 million people in the United States Southwest with their daily water supply and is unable to meet the current demands. New approaches are needed to enhance sustainability and resilience. A net zero urban water (NZUW) approach meets the needs of a given community with a locally available and sustainable water supply, without detriment to interconnected systems and the long-term water supply. Transitioning to a NZUW future will require considerable modifications to governance and policy across the Southwest and its cities specifically. We identify five areas of governance and policy challenges: diversified water sources and sinks; planning, design, and operation; monitoring and enforcement; coordination; and addressing equity and justice. Four case study cities are investigated: Albuquerque, Denver, Los Angeles, and Tucson. Across these cities, the policy priorities include supporting potable water reuse, coordinating policies across jurisdictions for alternative water sources, addressing equity and justice, developing and incentivizing water conservation plans, and making aquifer storage and recovery projects easier and more economical to pursue. We conclude that a NZUW transition in the Southwest faces considerable governance and policy challenges, but moving cities toward this goal is crucial. 

Researchers and practitioners from Albuquerque, Denver, Los Angeles, and Tucson convened virtually in November 2023 to discuss the development of NZUW model and integration of alternative water sources. The workshop was held in two sessions spanning two days, November 6th and November 17th, 2023. The first session aimed to identify the key questions that the NZUW model seeks to address and to prioritize scenarios for further investigation. It also focused on the challenges, adaptive solutions, and modeling needs for the 3 systems (natural, built and social) to be incorporated into the model. The second session delved into modeling methods used by previous studies to model urban water systems that integrate alternative water sources, to achieve objectives such as climate robustness, cost efficiency, and supply reliability (Porse et al., 2017; Newman et al., 2014; Bichai et al., 2015; Xu et al., 2020). This brief first outlines the common scenarios across the four case study cities that need to be modeled to achieve net zero water targets. It then details the challenges, adaptive solutions, and modeling needs within the natural, built, and social systems to be incorporated for model development (See Table 1). It further discusses the unique perspectives of each city and how their situations diverge from the collective findings. Finally, we present a summary of modeling approaches used by sample past studies for modeling urban water systems with alternative water sources, to offer insights for NZUW model development (See Table 2). 

This policy brief synthesizes the findings from a three-day workshop held at University of Arizona in April 2023, focused on identifying the governance and policy challenges to a NZUW future in the Southwest US. The workshop involved water managers, non-governmental organizations, and academics from across the Southwest, and was part of a four-year National Science Foundation Research Coordination Network (RCN) grant under the Dynamic and Integrated Socio-Environmental Systems (DISES) Program. The ultimate purpose of this DISES-RCN is to define and examine the viability and value of pursuing a NZUW approach in arid and semi-arid urban scenarios of Albuquerque, Denver, Los Angeles, and Tucson, all serviced by the Colorado River. A NZUW approach meets the needs of a given community with a locally available and sustainable water supply, without detriment to interconnected systems or long-term water supply (1). It is an integrative approach that uses progressive targets and a quantitative assessment framework to adapt to challenges created by multiple drivers of change in the urban water system. The findings detailed in this policy brief have been published in a recent ACS ES&T Water article titled “Advancing a Net Zero Urban Water Future in the United States Southwest: Governance and Policy Challenges and Future Needs” (2). This RCN is spearheaded by the University of Arizona, Colorado School of Mines, Colorado State University, University of New Mexico, and University of California Los Angeles, in collaboration with Tucson Water, Denver Water, Albuquerque Bernalillo County Water Utility Authority, and Los Angeles Department of Water and Power. The NZUW research network aims to improve the sustainability, resilience, and adaptation of urban water systems impacted by the Colorado river crisis and the recent reductions in their water allocations imposed by the Bureau of Reclamation (3).