To provide a method and facility for water treatment with the steam system and the water-supply system that maintains the hydrazine concentration of the entrance of a boiler economizer and reduces an oxidation scale concentration with a steam system as a center without sacrificing the deoxygenation effect, prevents the increase of the shaft power of a boiler water-supply pump and vibration problems, and protects equipment and pipes in a water-treatment facility.

In a water-treatment method for performing volatile water treatment by injecting ammonium and hydrazine, targeting for a water-treatment facility 13 with a steam system C for treating the exhaust of a steam turbine in a steam-power station and a water-supply system D, ammonium is injected into the steam system C and hydrazine is injected into the water-supply system D. The hydrazine injection part may be provided at the discharge side of a deaerator 20 instead of the discharge side of a boiler water-supply pump 21 in the water-supply system D.