Water use at nuclear power plants is essential for the safe, reliable, efficient, and sustainable operation of power facilities. The purpose of the research is to analyze the compliance with water use, temperature influence, and pollutant discharge into the surface waters of the Styr River at the Rivne Nuclear Power Plant. The research was based on long-term average data of environmental and operational factors of the power plant, using classification and generalization approaches, computational mathematical methods, and assessment of compliance with current water quality standards. The positive effect of lime softening on the reduction of cooling water replenishment consumption by up to 30% in different seasons has been demonstrated. The absence of temperature effects of return cooling water discharges on the environment was proved, the value of which was 1.07 ± 0.64 ℃. Cooling water quality was monitored and it was found that there is no negative impact on the structural materials of the cooling system and low-scale formation, which are explained by the fact that the actual values of water quality indicators to the results of monitoring over long periods are 1.0 times lower than the standard. The elements of an effective water management system for the cooling system of the Rivne Nuclear Power Plant are proposed to solve environmental and technological problems. The practical value of the research lies in the possibility of applying the methods to other nuclear power plants.