Dual water systems are becoming an important urban water management strategy as more utilities adopt increasingly integrated approaches that enable matching source water quality to the intended use, more efficient use of resources, use of nontraditional local water sources, and more resilient systems. Four alternative strategies for the dual supply of raw water for nonpotable municipal uses (e.g., landscape irrigation and fire supply) and treated water for potable uses were evaluated in this study. The alternative strategies included centralized and decentralized water treatment approaches, varying distribution system scales, and integration of existing irrigation ditches with raw water landscape irrigation systems. Multiple criteria decision analysis (MCDA) was used to conduct a triple bottom line (TBL) evaluation of the alternative strategies versus maintaining a conventional water supply system. This methodology allowed for the inclusion of incommensurable performance indicators and stakeholder preferences in the decision process, which was instrumental in garnering stakeholder support. The study found that the alternative strategies provide many social and environmental benefits versus a conventional system that may justify initial capital costs; a predominately gravity-fed distribution system favored centralized water treatment alternatives to decentralized options, existing irrigation canals for municipal use provide unique social and environmental benefits important to the community, and the optimum strategies are dependent on local conditions and community priorities.

The historical division of water management into different sectors, with financially and technologically driven decision processes, makes taking a more holistic approach to finding sustainable solutions for urban water management difficult. Here, a planning framework for Integrated Urban Water Management (IUWM) that evolved during a two-year study evaluating alternative strategies for dual water supply within a local government context is described. The planning framework was developed to overcome the obstacles that surfaced over the course of the study. It provides a structured approach to strategic decision making that integrates triple bottom line (TBL), multi-criteria decision analysis (MCDA), uncertainty and sensitivity analyses, and participatory decision making into an exploration of water supply alternatives. TBL assured stakeholders that the decisions considered the financial, social, and environmental performance. MCDA provided visibility into the benefits and trade-offs of the alternatives by providing a quantitative method for comparing alternatives that incorporates incommensurate performance indicators and priorities of multiple stakeholders. Uncertainty and sensitivity analyses addressed concerns regarding decision risk and improved transparency into inputs driving uncertainty in the analysis. Finally, a flexible participatory process helped to circumvent socio-institutional barriers by adapting the methodology and increasing cooperation among stakeholders and multidisciplinary experts. The resulting collaborative, risk-informed, TBL-MCDA (CRTM) planning framework helps to refine the feasible set of alternatives by providing more transparency into the drivers, technologies, and stakeholders influencing the decision. The planning framework increased the number of participants that were involved in the study, increased interaction between participants, changed the structure of the decision problem, increased the number of performance indicators considered, and improved stakeholder cooperation in the decision process.