<p>The effect of climate change on water availability is a growing concern for decision-makers involved in resource management, as well as within the hydrological and hydraulic engineering communities. To ensure the resilience of water supply systems, it is essential to adapt the sustainable and integrated management of drinking water sources to the expected changes in the magnitude and occurrence of hydrological droughts. This paper introduces a methodological framework for the sustainable management of water resources in a coastal region of Northern Italy under climatic change, aimed at modelling a multi-basin water supply reservoir, which represents the primary and most sustainable source of the system. The approach involves the multi-objective optimization of its withdrawal rules under both historical and future meteorological forcings, aiming to maximize reservoir production while meeting the demand during water scarcity conditions. The reconstruction of the historical operation of the dam controls and the estimates of the reservoir minimum demand requirements further support the implementation of the methodology. Utilizing a Parameterization-Simulation-Optimization approach and a wide range of climate models, the findings offer valuable insights to support decision-makers. Specifically, the research quantifies future expected relative changes in optimal operating rules based on different management policies. It also outlines the corresponding expected patterns of withdrawal volumes and potential water system failures throughout the century. This information allows to effectively assess the risk associated with future water scarcity and aids in developing long-term resource management strategies, thereby mitigating stress on less sustainable water sources.</p>