Water feeding method, water feeding system implementing said method, and steam generating facility provided with water feeding system

A water feeding system, comprising:

• a first feed water line through which first feed water flows;
• a second feed water line through which second feed water having a lower pressure than the first feed water flows;
• a first heater configured to heat the first feed water;
• a first feed water introducing line configured to guide first heated feed water which is the first feed water heated by the first heater to the second feed water line;
• a medium heat exchanger provided in the first feed water introducing line and configured to cause the first heated feed water to exchange heat with a medium, thereby cooling the first heated feed water and heating the medium;
• and
• a cooling water injecting line configured to inject cooling water into the first feed water introducing line at a position located further to the second feed water line side than the medium heat exchanger, the cooling water having a lower temperature than the first heated feed water.