It is known that thioglycolic acid (TgA) is widely used in industry and, unlike many other thiols, has a negative influence on organisms, similar to cysteine (Cys). The goal of this work was to study the TgA photochemical transformations in waters using model systems and to determine the kinetic parameters by varying the irradiation sources. It was found that TgA undergoes destruction on induced photolysis in the presence of humic substances (HSs), and its half-life can be estimated as 10-14 days, depending on weather conditions (cloudiness, time of day, season etc.). Results obtained in the course of this study on model systems were transferred to natural waters, and it was concluded that TgA has a positive influence on the chemical self-purification processes of water, in the natural aquatic environment. This is manifested by increasing the self-purification capacity of water, due to the generation of active oxygen species (ex.: O2¯•, •OH, 1O2), which lead to the degradation not only of this thiol, but of other pollutants present in aquatic environment, as well. At the same time, the products of the transformations are harmless to the aquatic environment and hydrobionts.