Based on data gained from the Kostak public utility company in the town of Krško, this graduation thesis analyses the impact of contaminants on drinking water. In the first part, the legislation on drinking water is presented. This is followed by a brief description of water system in Krško, which includes 3 water resources located in two separate locations. The Brege and the Drnovo pumping stations are situated in the Krško polje (the Krško field), where the impact of farming, industry and traffic is the highest. Rising nitrate and pesticide levels pose a serious problem. The Rore pumping station is located in the Krško hribovje (the Krško hills) and is one of the least polluted water resources in the entire municipality of Krško.