Enhancing Urban Water Security through Multiobjective Optimization of Alternative Water Supply Systems: A Case Study of Greater Melbourne, Australia

Urban water security faces unprecedented challenges from climate change and population growth, necessitating innovative approaches to alternative water supply (AWS) integration for sustainable water security resilience. Although previous studies have explored individual alternative water sources, limited research has addressed the optimal integration of multiple decentralized and centralized sources under long-term uncertainty. This study aims to apply multiobjective metaheuristics algorithms to identify optimal mixes of desalinated water, recycled water, and household rainwater tanks in Greater Melbourne, Australia. The model evaluates tradeoffs between economic cost and greenhouse gas (GHG) emissions. Comparative analysis against the multiobjective water cycle algorithm (MOWCA) and established algorithms [multiobjective particle swarm optimization (MOPSO), Non-dominated Sorting Genetic Algorithm II (NSGA-II), and multiobjective differential evolution (MODE)] demonstrated that MOWCA achieves superior performance across the planning horizon. MOWCA demonstrates the strongest convergence (generational distance = 0.007–0.08), outperforming MOPSO (1.51–2.06) and NSGA-II (0.37–1.87), and aligning slightly with MODE (0.05–0.08). It is also the most computationally efficient, averaging 67.7 s per run, substantially faster than MOPSO (101.6 s), NSGA-II (132.3 s), and MODE (141.7 s). MOWCA attains the lowest constraint violation (MAPE = 0.08%) and achieves 8–14% lower total cost under high-demand conditions. It also delivers comparable GHG emissions, yielding a superior balance between economic and environmental objectives. Results reveal optimal supply portfolios prioritizing recycled water (10–30%) and rainwater harvesting (29–49%) over energy-intensive desalinated water (20–43%). The methodology developed provides a framework for cities globally facing similar water security challenges, offering approaches to AWS integration that balance economic efficiency with environmental sustainability for long-term water security. Findings demonstrate that decentralized and climate-independent alternatives can reduce reliance on traditional centralized systems while ensuring urban water security under uncertainty.