Analysis of Natural Water Quality in the Dniester River Basin for Economic Utilization

Small rivers and other surface and groundwater sources form the basis for the functioning of river basin systems, shaping streamflow, providing water supply for rural areas, and supporting biodiversity. Local surface and groundwater sources are extremely sensitive to anthropogenic impacts and climate change. Changes in the quality and quantity of water in these sources are a primary factor influencing their use for various purposes, objects, methods, and technical conditions. Therefore, the research aimed to assess the quality of natural waters in the southern part of the Mohyliv-Podilskyi district, within the basin of the small river Kotlubayevka (a right tributary of the Dniester River). The primary research methods were analytical and statistical. The analytical method was used to determine the chemical composition of water samples according to standardized procedures. The statistical method was used to find out the reliability of measurement results and to provide a generalized assessment of water quality. Experimental results were processed for water samples based on ecological and sanitary criteria from eight potential sources of economic use located along the slopes of the Dniester and Kotlubayevka river basins, ranging from elevations of 215–206 to 78–55 m a.s.l. According to the ecological classification of surface water quality, the studied sources are classified as fresh oligotrophic (class I), and based on ion composition criteria, they are categorized as bicarbonate waters of type I ( $${\text{HCO}}_{3}^{ - }$$ > Ca2+ + Mg2+). The study identified a trend of water source contamination in the research area concerning copper, iron (Fetotal), and saprophytic bacteria Escherichia coli. A generalized ecological assessment of water was calculated using block indices for salinity composition, ecological-sanitary, and specific toxic indicators, which ranged from 2.33 to 3.00 along the slope above the river currents. The results indicate that the quality of the studied water sources ranges from “very good,” “clean,” to “good,” “fairly clean.” However, based on the block index for specific toxic indicators, the water quality tends to approach “fairly good” or “slightly polluted.” Among the water contaminants, elevated levels of Fetotal, Cu2+, and E. coli primarily contribute to the deterioration of water quality and safety. Iron and copper contamination should be regarded as a natural factor, while microbiological contamination by E. coli should be considered a result of anthropogenic impact. The obtained research results impose limitations on the economic use of certain water sources, particularly in agricultural production.