The subject of this doctoral dissertation is to examine the impact of natural and anthropogenic factors on the water quality of the Vrbas River, which is used as a drinking water resource in the city of Banja Luka. Identified potential negative natural factors are sudden heavy rainfall, flood waves and the appearance of algae, while human activity factors are the discharge of wastewater, the discharge of upstream reservoirs and the collection of floating debris. In the conditions of significant influence of factors on water quality, the efficiency of drinking water preparation system at industrial and pilot plant was determined. Accordingly, the experimental part of the research included the analysis of Vrbas river water as a drinking water resource and the analysis of water as a finished product after the treatment. The analysis of historical data of the last six decades on meteorological conditions in the Vrbas River Basin, established an increase in air temperature in the last two decades by about 2 °C as well as extreme rainfall (up to 1686 l/m2). Changes in seasonal precipitation patterns were observed, ie. Occurrence of longer-lasting precipitation in the summer, which mostly affected the values of water turbidity. Therefore, in order to establish the relationship between rainfall and high values of water turbidity as well as predictions for the future, a short-term model of neural networks was applied. By applying this model, using the results of 2-hour measurements of river water turbidity, changes in the values of a given parameter can be successfully predicted for the period of the next 40 h. An increase in rainfall above 6 l/m2 can be considered an alarm for early warning of deteriorating water quality of the Vrbas River. Although in the last decade a lower degree of trophicity of Lake “BoÄ�ac” was noticed in relation to previous years, the period after the appearance of the flood wave is characterized by the largest number of silicate algae (26 taxa). During the period of algae emergence on Lake BoÄ�ac, the dominant species was Pyrrophyta (4 taxa and 194 individuals), and the high production of algae biomass was indicated by the content of chlorophyll-a (1770 mg/m3) and dissolved oxygen (16,2 mgO2/l). In the same period, the dominant species in the water intake was Bacillariophyta (25 taxa and 11055 individuals), with water turbidity >300 NTU. During the period of sediment removal from the “Jajce II” accumulation, nickel had the highest value (77,4 µg/l Ni). The content of ammonium and nitrite ions is significantly increased in relation to the previous removal of sediment from the accumulation, which may indicate the aging of the accumulation, ie an increase in its turbidity. Removal of ammonium ions in the process of water treatment by conventional process was bad for the input values >1,0 mgNH4+/l, which caused its appearance in drinking water. Nitrite ion removal was significant (up to 97%) for the entire range of detected values. The application of ozone (pilot plant) at any dose did not significantly affect the ammonium ion content in the water, while the removal of nitrite ion was complete. Biological removal of ammonium and nitrite ions was performed at a filtration rate of 0,8 m/h and at a hydraulic retention time on the biofilter of 1,5 h, in the temperature range of 7,1-9,8 °C. When biomass was already formed, increasing the filtration rate did not significantly affect the nitrification process. The results of the examination of the microbiological quality of the Vrbas River flow indicate the impact of wastewater as a source of pollution and the need for a more responsible approach in the sanitary protection of the water intake itself as well as the site upstream of the water intake. Gas-chromatographic analysis of Styrofoam identified a larger number of organic compounds (47) compared to plastics (28). Heptachlor (1274,41 µg/kg) and naphthalene (518 µg/kg) had the highest concentration, which were detected on styrofoam. Naphthalene was also detected in water (53,2 ng/l), which indicates that it was sorbed from water onto the styrofoam surface. The large variability in the turbidity of raw water during the period of discharge of the reservoir also caused suboptimal coagulation conditions, which resulted in increased turbidity after the main and final clarification process (>1 NTU). The use of low doses of polyelectrolyte (0,1 mg/l) with the use of aluminum sulfate, makes the process significantly more efficient, especially for the input turbidity of raw water of 10-25 NTU.