Our paper presents the possibility of applying the DRASTIC model as a useful tool to support the process of local and regional development planning. The study was carried out in the catchment of Stare Miasto Reservoir in Central Poland. In order to plan the policy to protect the reservoir and groundwater, the assessment of groundwater vulnerability to pollution was made by means of the DRASTIC model. The original model was modified by adding a new parameter called “land use.” The measured nitrate concentrations were used to test the original and modified models. The results of the study revealed that the modified DRASTIC model gave more accurate predictions than the traditional model. The Pearson correlation coefficients characterising the relationship between the vulnerability index and the nitrate concentration was 0.56 before the modification and 0.69 after it. The groundwater vulnerability map is necessary for planning local development and for assessing environmental impact. The DRASTIC model is expected to be a useful tool for designing programs and strategies, e.g., for improving the quality of surface water and groundwater.