To provide water to be electrolyzed and raw water for water to be electrolyzed which can suitably used for electrolysis, by inexpensively removing components having a bad influence on the electrolysis, contained in the water to be electrolyzed with a simple method.

A method for preparing the water to be electrolyzed, used for the electrolysis or the raw water for the water to be electrolyzed, used for the preparation of the water to be electrolyzed comprises the treatment of general water by a cation exchange means and treatment of the treated water by an anion exchange means. A cation exchange resin selected from a group consisting of H type, Na type, and K type ion exchange resins is used as the cation exchange means. An anion exchange resin selected from a group consisting of OH type, Cl type, and SO4 type ion exchange resins is used as the anion exchange means.