Graphical Abstract: This paper presents the the main scientific and innovative results are presented, which were obtained by the talented chemist and renowned ecologist Valeriu Ropot throughout his scientific career. The results of scientific investigations are bestowed and analysed concerning the quality of the waters of the Dniester and the Prut Rivers, Dubasari reservoirs on the Dniester River, as well as the main bodies of water in the Republic of Moldova. The paper also includes the practical recommendations for reducing the negative impact on the environment, of the discharge of hundreds of thousands of tons of brine into the Dniester River as a result of the accident at the mineral fertilizer plant in the city of Stebnik, Ukraine. Moreover, the paper presents the results of studies aimed at developing methods for determining organic and inorganic pollutants in natural waters.