Abstract: A flow meter includes a lower shell flow meter includes: a lower shell; an upper shell disposed on the lower shell; a running water cavity disposed between the lower shell and the upper shell; and an impeller disposed in the running water cavity. The impeller includes: an installation positioning hole disposed at a bottom portion of the impeller; and a rotating positioning hole disposed at a top portion of the impeller. The flow meter includes an installation positioning shaft extending upward from the lower shell and configured to be inserted into the installation positioning hole; and a rotating positioning shaft extending downward from the upper shell and configured to be inserted into the rotating positioning hole.