Fuel filter system particularly for motor vehicles and method for its operation

A fuel filter comprises a filter housing with a fuel inlet and a fuel outlet, a filter element for cleaning fuel accommodated in the filter housing, and a water discharge device provided in the housing. The water discharge device comprises a discharge device housing with a water discharge inlet, a water discharge outlet and a water permeable membrane which has channel structures which are closed in a sealed manner at their upper ends. The fuel filter comprises a filter housing (10) with a fuel inlet (14) and a fuel outlet (15), a filter element (16) for cleaning fuel accommodated in the filter housing, and a water discharge device (23) provided in the housing. The filter housing includes a collecting space (20) for collecting water separated from the fuel. The water discharge device comprises a discharge device housing (24) with a water discharge inlet (33), a water discharge outlet (28) and a water permeable membrane (25) arranged between the inlet and outlet. The water permeable membrane has channel structures (26) which are closed in a sealed manner at their upper ends. An independent claim is included for operating a fuel filter.