The development of hydrochemical passports for rivers represents a key step toward better understanding and managing water resources in Ukraine. The objective of this research is to assess the state of surface waters and forecast changes in the water area of the city of Mykolaiv. This is achieved by determining sampling points within the water area of the Buzky Estuary, the Southern Buh and Inhul rivers, and within the districts of Mykolaiv. The analysis includes examining integrated hydrochemical indicators and investigating the temporal and spatial changes in water quality. The research focuses on the regularities of changes in water quality over time and space and includes surface waters of the Buzky Estuary, the Southern Buh River, and the Inhul River within Mykolaiv. Photometric method for determining water quality indicators using the eXact Strip Micro 20 long-wave photometric system. Mathematical methods include statistical data processing, the method of average values in determining the level of surface water pollution, and graphical reflection of data for qualitative visual evaluation of results using MS Excel software. The level of mineralization varies between different observation points, but the general trends remain similar. The data indicate a significant excess of the maximum permissible concentration at all observation points, which is a serious reason not to use these waters as a source of technical and even more so drinking water supply. Alkalinity significantly exceeds the maximum permissible concentration in all months considered, which indicates a consistently high level of this indicator in water. There is an increase in alkalinity from December to March, after which there is a sharp drop in April, and in May it rises again. The regression analysis found that annual hydrochemical indicators dynamics correspond to the sine wave of long-term fluctuations. The resulting function has made it possible to predict fluctuations over 6 years of a sine wave.