The invention relates to a membrane filter for water treatment, comprising a head piece including a permeate collecting chamber with a permeate outlet, and at least one fiber bundle made from capillary membranes, which are secured into the head piece with an end that is open towards the permeate collecting chamber and sealed on the opposite end thereof. The head piece contains an air duct to which the mouth piece that protrudes into the fiber bundle is connected with at least one air outlet. At its other end, the fiber bundle terminates in freely movable manner in the untreated water.