An alkaline electrolyte solution is electrolyzed by a diaphragm-less electrolyzer to provide electrolytic water as purging and disinfecting water. The alkaline electrolyte solution is a mixture of at least one alkaline electrolyte selected from caustic sodium carbonate, caustic potassium carbonate, phosphorous sodium carbonate and sodium hypochlorite, and at least one neutral salt selected from sodium chloride, potassium chloride, sodium bromide and potassium bromide. The purging and disinfecting water is added to a water circulatory system. The result is that contaminants and noxious chemicals in the circulatory system are oxidation decomposed to thereby purge the circulating water, and noxious microorganisms such as germs, yeasts, fungi, and viruses, growing in the water circulatory system and causing degradation of water or development of slime are disinfected and thereby purged from the water circulatory system. The purging and infecting method can be carried out in a simple manner with minimum cost.