A central water purification system equipped with a sterilization unit for producing sterilizing water containing silver ions using electrolysis is provided to simplify structure of the system, reduce manufacturing costs of the system, and improve freedom degrees of installation and replacement of the system, a method for sterilizing the system is provided, and a method for cleaning the system is provided. A central water purification system comprises: a supply pipe(10) for supplying raw water; a first filtration unit(20) for primarily purifying or filtering raw water; a filtered water supply controller(30) for transferring purified filtered water; a second filtration unit(40) for filtering filtered water again; a water storage tank(50) communicating with a first discharge pipe(54) and a second discharge pipe(56) to receive and store purified water; a purified water supply unit(60) including a hot water tank(62) connected to the first discharge pipe of the water storage tank and a cold water tank(64) connected to the second discharge pipe; a drain line(70) for discharging purified water stored in the cold water tank of the purified water supply unit to the outside; a sterilization unit(80) for supplying sterilizing water into the water storage tank; and a controller(90) for controlling the filtered water supply controller, a valve(72) of the drain line, and the sterilization unit.
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