PURPOSE: To provide a control method for an automatic water supplier, practical at a low cost, wherein a pump expected to stop in a parallel operation mode can be automatically and surely paralleled off as necessary regardless of constitution of the pump itself.

CONSTITUTION: In a control method for an automatic water supplier of switching an operation mode to alternate operation A and parallel operation B, a pump in the parallel operation mode B is selectively and intermittently operated to decelerate as shown by Al → A2 → A3. In the selected pump, since a delivery pressure and a delivery flow amount are decreased by decelerating operation, the pump is stopped, when the delivery flow amount (q) is decreased to a predetermined value Q0 or less, in a parallel-off region and not stopped, since a water pressure H in a supply water flow path is decreased to the above- mentioned predetermined value H1 or less before the delivery flow amount is decreased to the predetermined value Q0 or less, in a nonparallel-off region, and the pump is stopped when decreased to the parallel-off region while decelerating operation is intermittently repeated.