Abstract: In a water treatment system with a function of filtering raw water, a filter can be securely and efficiently sterilized without using dangerous chemicals such as hydrochloric acid and sulfuric acid.

Abstract: Electrolytic water produced by controlling the electrolytic degree of electrolytic water discharged from an electrolyzer having anode and cathode chambers partitioned by an ion-permeable barrier membrane so as to produce electrolytic water having the desired pH value in accordance with the pH value, electric conductivity, oxidation-reduction potential, and ion concentration. The electrolytic degree of the electrolytic water is controlled by injecting a regulated electrolyte solution into raw water to be supplied into the electrolyzer, regulating the flow quantity of the raw water and/or the electrolytic water discharged from the electrolyzer, and/or varying the capacity of the anode and/or cathode chamber.