To provide a method and an apparatus for uniforming temperature by a water supply system.

The water supply system includes an underground water pipe 103 buried into an underground layer, and a closed water pipe 121 made of a closed pipeline laid on the ground. Underground layer temperature energy from the underground water pipe 103 is circulated by a water flow through the closed water pipe 121 to equalize temperature energy from a deeper underground layer to the temperature energy of a subject on the ground surface to which temperature energy is to be transferred, after which heat transfer is carried out.