The possibilities and application of GIS in the protection of drinking water sources are shown on the example of the Bulaž spring. In the first part of the paper, the sanitary protection zones (ZSZ) of the water source, their role and the method of their determination according to the current regulations are described. An overview of the geographic information system (GIS), its advantages in the context of spatial data collection and analysis, is also given, and the QGIS software used in this work is described. The natural characteristics of the Bulaž spring basin are described and analyzed, and an overview of the previous and existing sanitary protection zones of that spring is given. For the purpose of a more detailed analysis of the existing zones of sanitary protection of sources, a pollutant cadastre was created and analyzed on the areas they cover. The data was taken from available sources: the location of the settlement was determined based on the digital orthophoto (DOF) available through the Web Map Service (WMS), while the population data were taken from the last population census (in 2021) of the State Bureau of Statistics, roads were taken from OpenStreetMap (OSM) database, agricultural areas are spatially and attribute-defined in the CORINE Land Cover (CLC) database of land use and purpose as part of the Copernicus program, and other pollutants are taken from the Register of Environmental Pollution via WMS. Pollutants taken in this way are grouped by individual zones. Based on the analysis, a conclusion was made with the advantages and disadvantages of using QGIS software.