An apparatus for supplying water containing dissolved gas comprising a flowmeter for measuring a flowrate of pure or ultra-pure water and a mechanism for controlling a flowrate, a means for adjusting an amount of water which adjusts an amount of the pure or ultra-pure water supplied to the apparatus for dissolving a gas, a tank which receives the water containing dissolved gas in an excessive amount which is not used at a point of use, a piping system through which the water containing dissolved gas glows from the tank towards the point of use and the water containing dissolved gas in an excessive amount returns to the tank, a piping system for supplying the water containing dissolved gas to the tank, and a controlling means for adjusting an amount of water based on a water level in the tank.