PURPOSE: To provide a water supply system excellent in reliability, which is able to surely detect any trouble in a pump without requiring any special parts, and thereby to avoid any defective water supply without increase in cost.

CONSTITUTION: An operating number of pumps 1 and 2 is controlled according to water pressure or flow rate in feed water pipes 6 and 7 as replacing the operational sequence of these pumps 1 and 2 with each other. Any trouble in the pump 1 or 2 is detected from a time variation in the operation number of these pumps 1 and 2, and in time of detection, the effect is displayed on an operating display part 30, while the defective pump is stopped but operation by the remaining pump remains continued.