Centralized and Decentralized Strategies for Dual Water Supply: Case Study

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.