Air-permeable and water-permeable baffles in the form of a fine-meshed grill are mounted in front of the upwardly projecting side walls in a motor vehicle fresh-air intake duct in order to improve separation with an inlet grill retaining any coarse impurities and with at least one drainage aperture, located in the area of the lowest point of the fresh-air intake duct, for liquid separated out from the air current. The liquid making its way through the meshes of the grills flows, in the flow vacuum between baffle and side wall at the back of the baffle, downwards to the duct bottom and the drainage aperture.