A backwash filter system includes a filter array comprising a plurality of filter units each having a housing, a filter element unit and a process liquid inlet port and a filtered liquid outlet port connected respectively with process liquid inlet and filtered liquid outlet sides of the filter element unit for filtering process liquid. A process liquid inlet header connects to the process liquid inlet ports of the filter units. A filtered liquid outlet header connects to the filtered liquid outlet ports of the filter units. A first valve unit on the process liquid inlet header is switchable for connecting same alternatively to a process liquid source and a backwash liquid drain. The filtered liquid outlet header can communicate with a filtered liquid receiver.