Safe drinking water is a basic requirement for good health. Fresh water is already a limited resource in many parts of the world. In the next century, it will become even more limited due to population growth, urbanization and climate change. Purpose. Provide a comprehensive assessment of the water quality of the Kaniv Reservoir based on the calculation of the Water Quality Index (WQI). Methods. Analytical-synthetic method, geo-information (cartographic modeling), analysis of information sources, mathematical modeling. Results. There is an increase in BOD, COD and dissolved oxygen content in the area of the Kaniv Reservoir from the hydropost 500 m above the Bortnytsky Aeration Station (BAS) to the hydropost 2 km below the Kanivska Hydropower Station’s dam. The only exception is the hydropost 500 m below the BAS, for which the corresponding values are the largest, and the BOD indicator exceeds the established standards by 1.5 times. Ammonium content 500 m below BAS exceeds the standards established by Directive 98/83/EC by almost 3 times. Exceeding the normative values for the content of sulfates and chlorides and suspended substances were not recorded. The least polluted water is observed at hydrostations located below Ukrainka and Pereyaslav-Khmelnytskyi. The highest value of the water quality index is 242, which is typical for the hydropost 500 m above the BAS and corresponds to the value of the worst quality. Conclusions. It was in the immediate vicinity of the city of Kyiv that the water turned out to be the most polluted. This may indicate the imperfection of industrial, domestic and agricultural wastewater treatment systems. For the hydropost 500 m below the BAS, excesses of the normative values for the parameters of ammonium and BOD content were also recorded, while other parameters are either at the limit of the norm or approaching it. Studies of the water quality of the Kaniv Reservoir showed that its quality according to the WQI indicator varies from 59 to 242 (from low to the worst). Accordingly, such water, in the absence of another source, can be used for drinking after passing proper multi-stage purification.