PURPOSE: To simplify the structure of an apparatus by a method wherein water in a pressure tank equipped with an air chamber sealed up with a bladder is pushed out directly by a pressure applied with the bladder and is supplied to the inside of a building through an outlet.

CONSTITUTION: With the pressure of water in a distributing pipe 30, the water flows through a check valve 31 and an inlet piping 36 into a space between a bladder 23 and a resin layer 22 in a pressure tank 20, and is stored in the tank 20 to a level that balances with the air pressure in the bladder 23. The water stored in the tank 20 is pushed out directly through an outlet piping under the pressure applied by the air in the bladder 23, and is supplied to fuacets 11 in a building 10.