The invention relates to medicine, in particular to sanitary and hygiene, more specifically to methods for producing a disinfecting agent for decontaminating different types of water, including drinking water. The inventive disinfecting agent producing method by dissolving quaternary ammonium compounds in water in the presence of an active additive in the form of guanidines, consists in preparing an aqueous 1-15 % guanidine solution by permanently agitating it at a temperature ranging from 30 to 90 DEG C, in cooling the solution accompanied with a precipitation control, when the precipitation process is over, in filtering the solution by using a filter whose cell size ranges from 10 to 1 mkm and in adding the quaternary ammonium compounds into the solution in such away that the concentration thereof in said solution is equal to 0.1-3%.
