A water pump bearing unit for satisfactorily sealing an impeller side of the pump comprises a plurality of rollers installed in the annular space between a water pump shaft and a pulley respectively on one and the other ends thereof and an outer ring surrounding the shaft; an annular seal member with two lips, each having an interference, inwardly and outwardly extended in the axial direction between the end of the outer ring on the impeller side and the outer peripheral surface of the shaft; and an annular seal member with a lip having an interference inwardly extended in the axial direction between the end of the outer ring on the pulley side and the outer peripheral surface of the shaft.