Multi-Objective Water Network Optimization Under Shifting Reliability Perspectives

Water distribution systems (WDS) are critical urban infrastructures reliably delivering safe drinking water and supporting firefighting activities. When developing a system master plan, water utilities may choose-or be compelled by their environment-to prioritize different reliability perspectives, such as hydraulic, mechanical, or firefighting. Mathematical optimization can aid in system intervention planning, but accurate reliability assessments require many computationally expensive simulations. To reduce this burden, previous studies have proposed reliability surrogate metrics and explored their correlation with the actual definitions. Instead, this work examines how adopting different reliability perspectives in WDS optimization affects system design and the potential cost of misrepresenting a utility's planning perspective. This question is particularly relevant because of the long planning horizons, as deep uncertainties can affect utility priorities over time. Different bi-objective optimizations of the Anytown benchmark system are performed, each reflecting a distinct perspective that a water utility might adopt. The cost objective-always present due to tight budget constraints-is paired with another objective expressing the utility's most pressing concern: operational efficiency, reliability under pipe failures, or fire response capacity. An evolutionary algorithm seeks Pareto-optimal solutions for these WDS design optimization problems. Results show that each perspective prioritizes different network components at comparable budget levels. WDS design should prioritize hydraulic reliability and daily operational efficiency, treating other goals as constraints or secondary objectives to broaden design exploration.