Pollution of the reservoir - changes in the composition and properties of water as a result of natural process or under the influence of human activity, leading to changes in the regime of aquatic ecosystems and deterioration of living organisms and impossibility to use water bodies for water use. A distinction is made between primary and secondary pollution. The main pollutants are radionuclides, oil products, copper, nickel, zinc and iron compounds, phenols, phosphates, nitrogen compounds. The level of pollution is controlled by various regulations.

Changes in the chemical and physical state or biological characteristics of water that limit its further use. In all types of water use, either the physical state (e.g. heating) or the chemical composition of water is changed by the introduction of pollutants, which fall into two main groups: those that change over time in the aquatic environment and those that remain unchanged in it. The first group includes organic components of domestic wastewater and most industrial wastewater, such as waste from pulp and paper mills. The second group includes many inorganic salts, such as sodium sulphate, which is used as a dye in the textile industry, and inactive organic substances such as pesticides.