A fire truck operable to automatically refill a water tank comprises a first pressure transducer coupled to an intake inlet of the pump and operable to measure an intake pressure, a second pressure transducer coupled to a discharge outlet of the pump and operable to measure a discharge pressure, a first discharge pipe coupled between the discharge outlet of the pump and a fire hose, a second discharge pipe coupled between the discharge outlet of the pump and the water tank, a control valve disposed in the second discharge pipe, and a controller operable to automatically sense a low water level condition of the tank, and automatically control the engine speed, the pump speed, and the control valve so that adequate water supply to the fire hose via the first discharge pipe is automatically given priority and maintained while automatically refilling the water tank via the second discharge pipe.