To provide improved efficiency of sterilization treatment with hot water.SOLUTION: A method of sterilizing a pure water production apparatus 1 comprising: a membrane filtration device 3； and an electric deionized water production device 4 connected to the downstream side of the membrane filtration device 3 and supplied with permeated water from the membrane filtration device 3. The method has: a step in which, after the water to be treated from a pretreatment device stored in a water to be treated tank 2 is sequentially supplied to the membrane filtration device 3 and the electric deionized water production device 4, it is returned to the water to be treated tank 2, thus circulating the water to be treated along a circulation path including the membrane filtration device 3 and the electric deionized water producing device 4； and a step of heating the water to be treated circulating along the circulation path to a predetermined temperature, and then cooling it after held for predetermined time, thus sterilizing the membrane filtration device 3 and the electric deionized water production device 4. The step of sterilizing is performed within the range of the conditions that a cation exchanger CE and an anion exchanger AE packed in a deionization chamber D of the electric deionized water production device 4 are not broken.SELECTED DRAWING: Figure 1【課題】熱水による殺菌処理のさらなる効率化を実現する。【解決手段】膜ろ過装置３と、膜ろ過装置３の下流側に接続され、膜ろ過装置３からの透過水が供給される電気式脱イオン水製造装置４と、を有する純水製造装置１の殺菌方法は、被処理水タンク２に貯留された前処理装置からの被処理水を膜ろ過装置３と電気式脱イオン水製造装置４に順次供給した後、被処理水タンク２に還流させることで、膜ろ過装置３と電気式脱イオン水製造装置４とを含む循環経路に沿って被処理水を循環させる工程と、循環経路に沿って循環する被処理水を所定の温度まで加熱し、一定時間保持した後に冷却することで、膜ろ過装置３と電気式脱イオン水製造装置４とを殺菌する工程と、を含んでいる。殺菌する工程は、電気式脱イオン水製造装置４の脱塩室Ｄに充填されたカチオン交換体ＣＥとアニオン交換体ＡＥが破過しない条件の範囲内で行われる。【選択図】図１
