An apparatus for controlling a water pump having an engine that drives an impeller, a water storage tank connected to the water pump, a first water level detector that outputs an A signal when a water level is at or higher than a first height and outputs a B signal when lower than the height, a second water level detector that outputs the A signal when the water level is at or lower than a second height and outputs the B signal when higher than the height, a connection switcher that switches connection of the first and second water level detector, and an impeller controller connected to the connection switcher and adapted to control operation of the engine that drives the impeller of the water pump based on the signals outputted from the first and second water level detectors.