The invention relates to a filter device, in particular for fluids polluted with admixtures of water, such as diesel oil, comprising a filter housing (1) which has fluid connections in the form of a fluid inlet (51) and a fluid outlet and in which at least one filter element (9) can be received. During the filtering process, fluid can flow through the filter medium (11) of the filter element from the unfiltered side (13) to the filtered side (19) of the filter medium, which surrounds an inner filter cavity (17). On one side of the filter medium (11), a water-separating device (26) and a separating region (27) for separated water are present, and the filter element (9) has a passage (43) that forms a fluid connection to the filter cavity (17) and at least one water opening (47) that is open toward the separating region (27). The filter element can be fixed to an element receptacle (29) of the filter housing (1) and can be connected to a water collecting chamber (33). The filter device is characterised in that an adapter part (49) is provided at least as part of a fluid-conducting system, in which fluid paths separated from each other are formed, of which the first fluid path (59, 67, 61) leads from a fluid connection (51) of the housing (1) via the passage (43) to the inner filter cavity (17) of the filter element (9) and the second fluid path (69) connects the respective water opening (47) to the water collecting chamber (33).