A method of feeding pure water under germ-free conditions is provided by purifying raw water into primary water by successive passage through a defined series of purification units, temporarily storing the primary water in a primary water tank, further purifying the stored water to still higher purity by passage through a defined series of purification units; injecting HF or a salt of HF into the thus-purified water in bacteriostatic and sterilizing concentrations and then feeding it to its point of use.