To provide a sterilizing and antimicrobial method for circulated and reserved water which has a sufficient sterilizing effect, maintains a sterilizing and antimicrobial effect, has no influence on human health and is inexpensive.

The sterilizing method for the circulated and reserved water comprising sterilizing the inside of a water circulated and/or reserved water facility by an aqueous hypochlorous acid-containing solution of 0.2 to 1,000 ppm in an effective chlorine concentration and 2.0 to 8.0 in pH regulated by addition of an acid. In the antimicrobial method, the peripheries of circulated reserved water producing equipment contain an inorganic antimicrobial agent containing at least one kind among metallic ions consisting of Mn, Fe, Co, Ni, Cu and Zn.