Assessing Uncertainty in Multicriteria Evaluation of Centralized and Decentralized Dual Water Supply Strategies

Abstract

As much of our urban water supply infrastructure reaches the end of its useful life, water managers are using the opportunity to explore alternative strategies that enable them also to utilize alternative local water sources (e.g., untreated raw water, reclaimed water, graywater, and stormwater). However, evaluating alternative strategies is challenging because water managers are required to balance the needs of multiple stakeholders, consider all the costs and benefits, reduce risks, and, most importantly, ensure public health and protect the environment. Here, the benefits and trade-offs of dual supply of raw and treated water were assessed with consideration of centralized and decentralized options. The study resulted in a complex decision process involving 45 performance indicators and 17 stakeholders. Uncertainty and global sensitivity analyses were applied to the study's decision models to assess the reliability of the results given long-term uncertainty, improve transparency in the decision process, and elucidate the benefits and trade-offs of alternatives for dual supply of raw and treated water. The key drivers of model variance were regulatory and political, including access to alternative nonpotable water sources in the future, the ability to sell potable water to adjacent utilities, and the possibility of cost savings by avoiding the need for water rights conversion. Although technical considerations are important, the results reveal the importance of addressing regulatory uncertainty related to dual water supply systems and decentralized water systems. The decentralized alternatives were particularly sensitive to uncertainty in regulatory risks. Resolving these issues highlights the importance of including a wide range of local, regional, and regulatory stakeholders in the decision process.