<p>This study develops, for the first time, a Multi-Objective Slime Mould Algorithm (MOSMA) for the optimal operation of urban water distribution networks. The algorithm is integrated with EPANET 2.0 and generates a set of optimal solutions in the form of Pareto fronts. The benchmark Hanoi network and a real network in southern Tehran are examined to evaluate the performance of the proposed method. Two multi-objective formulations are considered: (i) minimizing cost and maximizing the Minimum Surplus Head (<i>MSH</i>), and (ii) minimizing cost and maximizing the Network Resilience Index (<i>NRI</i>). A Head-Driven Simulation Method (HDSM) is applied under three hydraulic scenarios (<i>H</i>^<i>min</i> = 5, 10, and 20 m). The performance of MOSMA is compared with NSGA-II, MOPSO, and SPEA-II using the Entropy Reliability Index (<i>ERI</i>) and the Pressure Performance Index (<i>PIP</i>). Results for the Hanoi network show that increasing <i>H</i>^<i>min</i> leads to higher <i>MSH</i> and <i>NRI</i> values and reduced surplus head, with MOSMA consistently outperforming the other algorithms. In the Tehran network, MOSMA improves surplus head and resilience under all hydraulic scenarios and provides more cost-effective pipe diameters. Compared with the benchmark algorithms, MOSMA achieves higher <i>ERI</i> and <i>PIP</i> values for both objective formulations, demonstrating superior convergence quality and operational performance. Overall, the proposed MOSMA framework offers an effective and robust tool for multi-objective optimization of water distribution systems.</p>