Abstract: A process of passivation of galvanized surfaces which are exposed to water, such as in open or closed water circuits where equipment with galvanized surfaces is exposed continuously or intermittently to circulated water solutions, as in cooling towers or evaporative condensers, characterized in that during all or part of the passivation operation, gaseous CO2 is injected in the water being in contact with the galvanized surface, and in that the CO2 injection allows to keep the pH of the water in the [7.0, 9.0] range, and preferentially in the [7.0, 8.0] range.