<p>Preserving groundwater quality is crucial for sustainable water supply, especially in light of the increasing water demand. This research aimed to select the optimal groundwater source protection plan for the new “Jagodica” source (Serbia) against potential contamination, using multi-criteria decision-making (MCDM) methods. Potential groundwater pollutants at this site include oil and gas extraction wells, which are part of the infrastructure of the Petroleum Industry of Serbia (NIS). During the research, numerical modelling data were first used to determine the general direction of groundwater flow and to identify critical locations where potential pollutants could threaten the natural water quality. Based on the results of hydrodynamic forecast simulations, three groundwater source protection management plans were defined for the highest risk scenario (during maximum surface water levels): drainage wells, a waterproof screen, and a drainage canal. To select the optimal plan, a multi-criteria analysis was applied within a rough numbers environment. Criteria weights were determined using the Level Based Weight Assessment (LBWA) method, while ranking was conducted using a new MCDM method - ranking of alternatives through functional mapping of criterion subintervals into a single interval (RAFSI method). Validation of the results included comparison with other rough MCDM methodologies, variations of the Bonferroni operator, and sensitivity analysis of the most influential criterion. The presented approach, which integrates hydrodynamic modelling results with advanced MCDM methods, represents an effective decision-making tool for managing groundwater pollution risks and can be applied to other locations with similar characteristics.</p>