This chapter studied the influence of TGA and TU on the self-purification processes of aquatic systems on model systems, whose composition was modeled to be as close as possible to the natural waters. As a source of irradiation was used the DRT-400 lamp and the Solar Simulator, Oriel model 9119X, the emission spectra of which overlap with the emission spectrum of the Sun. The results of the research show that on irradiation, TGA can regenerate an additional amount of OH radicals, thus contributing to the intensification of water self-purification processes. But in the presence of transition metals, such as Cu (II) and Fe (III), it has been established that the intensity of self-purification processes decreases due to the formation of the mercaptides, whose catalytic activity is low. Unlike TGA, TU leads to decreasing the intensity of the self-purification processes of aquatic systems, through the intense consumption of OH radicals, and at the same time on the interaction with transition metals, such as Cu (II) and Fe (III), form stable complexes with low catalytic activity.