In addition to their adequate quantitative status, good surface water quality is one of the key objectives of sustainable river basin management. In Slovenia, regular monitoring takes place on larger watercourses, while smaller ones are often excluded from this monitoring. This research presents an analysis of water quality on the Zasavje watercourses Medija, Trboveljščica and Boben, which are not included in the regular monitoring of water quality. These are small watercourses that are exposed to relatively high pressures due to the flow through larger urban settlements (Trbovlje, Zagorje and Hrastnik). Water quality was assessed on the basis of field and laboratory analyzes of selected physicochemical parameters (pH, water hardness, temperature, nitrate, nitrite, chloride, phosphate, sulfate, ammonium, fluorine, potassium, cationic detergents, electrical conductivity, oxidation-reduction potential, dissolved oxygen saturation, the amount of oxygen dissolved in water). In the period 2020–2021, we performed 9 cyclic sampling at 16 permanent locations. In the headwaters, water pollution is relatively low and mainly conected with agriculture. This is also shown in better overall water quality. On lower parts of streams, especially in Boben river basin, major role falls on industry and households.