Backflow filter for filtering drinking and water for other use which is adapted to be switched from an operating position where water is flowed from the inlet (14; 214) through the filter to the outlet (15; 216) to a backflow position for backflushing, where water is flowed from the inlet (14; 214) in reverse direction through the filter to an open drain (92; 292), comprising: (a) a connection fitting (12; 212) with an inlet (14; 214) and an outlet (16; 216); (b) a filter cup (30; 230) with a closable drain (94; 294); (c) a filter element (44; 244) moveably guided in an axial direction between an upper filter section (68; 268) and a lower filter section (66; 266) and an annular space (46; 282) around the filter element (44; 244) connected to the inlet; (d) means for separating the annular space (46; 282) in such a way that the lower filter section (66; 266) is connected to the inlet (16; 216) and flowed through from the outside towards the inside in the operating position and the upper filter section (68; 268) in the backflow position; and (e) an impeller (100; 300) rotatable around the longitudinal axis of the filter element (44; 244) within the filter element (44; 244) wherein water flows from the inside towards the outside in the backflow position through a reduced angular range of the lower filter section (66; 266); characterized in that (f) the upper filter section (68; 268) has a smaller diameter than the lower filter section (66; 266), whereby an annular shoulder (70; 270) is formed between the upper and the lower filter section, and (g) the impeller (100; 300) is fixed relative to the housing in an axial direction and is provided with a cylindric, upwardly open body having a diameter which is larger than the diameter of the upper filter section (66; 266) and smaller than the diameter of the lower filter section (68; 268). (a) a connection fitting (12; 212) with an inlet (14; 214) and an outlet (16; 216); (b) a filter cup (30; 230) with a closable drain (94; 294); (c) a filter element (44; 244) moveably guided in an axial direction between an upper filter section (68; 268) and a lower filter section (66; 266) and an annular space (46; 282) around the filter element (44; 244) connected to the inlet; (d) means for separating the annular space (46; 282) in such a way that the lower filter section (66; 266) is connected to the inlet (16; 216) and flowed through from the outside towards the inside in the operating position and the upper filter section (68; 268) in the backflow position; and (e) an impeller (100; 300) rotatable around the longitudinal axis of the filter element (44; 244) within the filter element (44; 244) wherein water flows from the inside towards the outside in the backflow position through a reduced angular range of the lower filter section (66; 266); characterized in that (f) the upper filter section (68; 268) has a smaller diameter than the lower filter section (66; 266), whereby an annular shoulder (70; 270) is formed between the upper and the lower filter section, and (g) the impeller (100; 300) is fixed relative to the housing in an axial direction and is provided with a cylindric, upwardly open body having a diameter which is larger than the diameter of the upper filter section (66; 266) and smaller than the diameter of the lower filter section (68; 268). <EOS>