Relevance. Currently, greenhouse complexes use water for irrigation from open surface sources (ponds, lakes, rivers) and underground water from wells, adding a return (drainage) solution to it. At the same time, water from both open sources and drainage solution often becomes a source of emergence and spread of phytopathogenic infection in greenhouses, which brings economically significant crop losses. In this regard, the need to develop guaranteed methods and methods for the disinfection of drainage water and water from open sources is relevant. One of the methods of water disinfection is the use of ultraviolet irradiation, but for the effective use of irradiation, it is necessary to ensure the minimum effective UV dose. This UV dose is typical for each pathogen.Results. Work was carried out to experimentally establish doses of UV irradiation that allow complete inactivation of vegetative cells and spores of bacteria and fungi (Agrobacterium tumefaciens, Pythium debaryanum, Fusarium oxysporum, Verticillium dahliae, Phoma destructiva) in a solution prepared on the basis of distilled water. A dose of UV irradiation of 40 mJ/cm2 ensured complete inactivation of the bacterial pathogen, and a dose of 60 mJ/cm2 showed complete inactivation of the pathogens of the studied fungal infections.