Abstract: A method of water supply for a building construction capable of preventing the deterioration of the water quality even when the water is not extracted over an extended period of time. The method includes the steps of: receiving water externally supplied to the building construction by a receiving reservoir; reserving the water received by the receiving reservoir by an upper reservoir located above the receiving reservoir; supplying the water through the water supply pipes leading the water from the upper reservoir to individual faucets located between the receiving reservoir and the upper reservoir from which the water can be extracted; and circulating the water in the water supply pipes by returning the water back to one of the receiving reservoir and the upper reservoir. The system performing this method is also disclosed.