Abstract: The present invention relates to a water pump in a vehicle. The water pump in a vehicle includes a pump cover which forms an upper side exterior appearance of the pump for housing an impeller to be rotated, a hollow rotor coupled on the same axis with the impeller to rotate altogether, and a housing coupled to the pump cover to house the rotor and a stator therein, wherein the pump cover includes a first rotation shaft extended toward the hollow in the rotor passed through the impeller, the housing includes a second rotation shaft extended toward the hollow in the rotor, the first rotation shaft has a communication hole formed therein to be in communication with the hollow, and the rotor has a communication passage recessed in a lower end portion thereof to a predetermined depth.