Surfactants are one of the main pollutants in natural waters. At a concentration of 1 mg/l they form a foam, which settle on the water surface, lowering the surface tension of water. Also surfactants are accumulated in sediments and adsorbed by suspended solids. The foam can not be removed in the process of waste water treatment. All this limits the exchange of gases between the water and the atmosphere and leads to the death of aerobic bacteria, which take part to the decomposition of organic waste and, consequently, causes difficulties in water self-purification. The presence of surfactants changes the chemical composition of natural waters and the natural course of their chemical and biochemical processes, renders depressing effect on aquatic biocenoses. Detergents cause the fish gill bleeding and suffocation. Warm-blooded animals suffer from a violation of chemical processes in the cell membranes, causing the death of many aquatic organisms. Thus, the surfactant lethal concentration for many fish is 3-5 mg/l, plankton - about 1 mg/l. A content of 120 mg/l of an anionic detergent, or of 71 mg/l of a cationic type detergent in natural waters acutely decrease the algae growth. At the same time it shall not be ignored the possible effect of the joint action of surfactants and other toxins entering into natural water, such as pesticides. The surface-active agents are used in the production of detergents such as washing powder, liquid soap, shampoo, fabric softener cosmetics, in preparing the emulsions. Their cleaning properties are due to the amphophilic structure of the molecule, surfactant consisting of a polar part (hydrophilic component) and a non-polar part (hydrophobic component). There are a range of groups of surfactants: anionic, cationic, nonionic, and amphoteric. World production of surfactants is increasing. Depending on the application and the chemical composition, the surfactants are produced in the form of solid (chunks, flakes, granules, and powder), liquid and semi-liquid materials (pastes, gels). Currently, in the top of list of produced surfactants the anionic ones are placed (alkilbenzosulfat, alkyl sulfate), followed by nonionic surfactants (alkyl polyglucoside). The maximum permissible concentration (MPC) of anionic surfactants in natural waters is 0.5 mg/l, and for nonionic - 0.1 mg/l. It should be noted that some of the anionic surfactants have a capacity of 80-90% biodegradation, but the most complete (almost 100%) biodegradation, which leads to the formation of water and carbon dioxide, have nonionic surfactants. Oxidation of surfactants consumes large amounts of oxygen, which reduces the disintegration of other harmful substances. Heterotrophic bacteria from genus Pseudomonas, which are part of active silt, also participate to the processes of biological oxidation of surfactants. According to the results of researches, in 2009-2013 on the territory of the Republic of Moldova the concentration of anion-active substances in the Prut River not exceeded the MPC (0.1 mg/l) [1, 2]. The determination of anionic surfactants was carried out by using spectrophotometry and applying standard SR EN 903, based on their action on methylene blue (MBAS) and subsequent measurement of absorption value [1].