A filter with a backwashing unit including a two-position three-way valve, and second third valves. The three-way valve has ports P1, A1 and B1, the second valve has ports P2 and A2, and the third valve has port P3 and port A3； port P1 is connected with the water inlet, port A2 is connected with the outlet, port A3 is connected with the drain outlet, port A1 and port P3 are connected with the inlet of a filter, and port B1 and port P2 are connected with the outlet； the filter is located on a filtering station when port P1 communicates with port A1, port P2 communicates with port A2, and port P3 does not communicate with port A3, and the filter is on a backwashing station when port P1 communicates with port B1, port P2 does not communicate with port A2, and port P3 communicates with port A3.
