In a water drain plug (10) for a cavity (16) of a vehicle, in particular a side sill (14), comprising a base body (18) which can be fixed in an aperture (12) of the cavity (14) and has an opening (20) in which a sealing element (22) is arranged that is adapted to be moved between a closing position in which the opening (20) is tightly closed, and an opening position in which the opening (20) is open, the sealing element (22) is mounted in the base body (18) for pivoting movement about a retaining axis (36).