Producing ultrapure water supply system and method cleaning

During sterilizing and washing, without supplying contaminants in ultrapure water production system to supply piping to the water points of use, also, after the sterilizing and washing, the system contamination by contaminants captured by the particulate filter membrane preventing, the short time for supplying ultra-pure water with good quality water point of use (POU). At least the tank 11, pump 12, heat exchanger 13, an ultraviolet apparatus 14, ion exchanger 15, the ultrapure water production system having a first particle removal membrane device 16, parallel to the first particulate filter membrane device 16 the second particulate removal membrane device 17 is provided in a portion of the sterile water and flushing water is supplied to the first particulate filter membrane device 16, and discharged from the water supply side to the concentrated water side without membrane permeation, the balance to to passed therethrough to the second particulate filter membrane device 17.