The present invention provides a water supply apparatus capable of performing a backup operation, without lowering water supply capability, when a failure has occurred in one control substrate due to surge or noise caused by lightning or due to lifetimes of various sensors, by switching to the other control substrate, and capable of reliably performing the backup operation by means of devices that prevent failure of the control substrates. The water supply apparatus (1) includes: a plurality of pumps (3); a plurality of inverters (INV) each configured to change and control a rotational frequency of a corresponding one of the plurality of pumps (3); and a plurality of control substrates (CN) configured to control the plurality of inverters (INV). When an abnormality occurs in one control substrate, other control substrate backs up the one control substrate to thereby allow the water supply apparatus to continue its operations. The one control substrate, the plurality of inverters (INV), and the other control substrate are connected in series by communication lines. A switch (SW1) for turning on and off a communication is provided on the communication lines.