A filter (10, 100) for filtering a flow of liquid, the filter comprising: a pressure vessel (12, 112) having an inlet (14, 114) and an outlet (16, 116); a filter assembly (18, 118) deployed within said pressure vessel, said filter assembly comprising a plurality of filter disks (20, 120) coaxially arrayed along a central flow path (22, 122) in fluid communication with said outlet, said filter assembly (18, 118) being rotatably mounted so as to be rotatable about a central axis, each of said filter disks comprising a spacer (19, 119) having first and second outward-facing filter screen support configurations (26, 126), and having an outlet (28, 128) for flow of filtered liquid inwards to said central flow path (22, 122), said first and second filter screen support configurations of said spacer supporting first and second filter screens (21, 121) forming corresponding first and second surfaces of each filter disk; and a backwash assembly (50, 150), characterized in that said backwash assembly comprises: a backwash arm (54 a, 54 b, 154 a, 154 b) extending between adjacent of said plurality of filter disks, said backwash arm terminating in a suction head (56 a, 56 b, 156 a, 156 b) comprising a suction nozzle (58, 158) in facing relation to one of said first and second filter screens (21, 121) and said suction head further comprising at least one rotatable roller (62, 162) deployed to provide rolling contact with said one of said first and second filter screens; a pivot arrangement (60, 160) for accommodating motion of said backwash arm so as to bring said suction nozzle (58, 158) into close contact with said one of said first and second filter screens (21, 121); and a drive arrangement (64, 164) configured to simultaneously rotate said filter assembly (18, 118) about said central axis and displace said backwash arm (54 a, 54 b, 154 a, 154 b) so that said suction nozzle (58, 158) moves through a range of radial positions on said filter disk, thereby causing said suction nozzle to follow a spiral tracking motion across a surface of said filter disk. a pressure vessel (12, 112) having an inlet (14, 114) and an outlet (16, 116); a filter assembly (18, 118) deployed within said pressure vessel, said filter assembly comprising a plurality of filter disks (20, 120) coaxially arrayed along a central flow path (22, 122) in fluid communication with said outlet, said filter assembly (18, 118) being rotatably mounted so as to be rotatable about a central axis, each of said filter disks comprising a spacer (19, 119) having first and second outward-facing filter screen support configurations (26, 126), and having an outlet (28, 128) for flow of filtered liquid inwards to said central flow path (22, 122), said first and second filter screen support configurations of said spacer supporting first and second filter screens (21, 121) forming corresponding first and second surfaces of each filter disk; and a backwash assembly (50, 150), characterized in that said backwash assembly comprises: a backwash arm (54 a, 54 b, 154 a, 154 b) extending between adjacent of said plurality of filter disks, said backwash arm terminating in a suction head (56 a, 56 b, 156 a, 156 b) comprising a suction nozzle (58, 158) in facing relation to one of said first and second filter screens (21, 121) and said suction head further comprising at least one rotatable roller (62, 162) deployed to provide rolling contact with said one of said first and second filter screens; a pivot arrangement (60, 160) for accommodating motion of said backwash arm so as to bring said suction nozzle (58, 158) into close contact with said one of said first and second filter screens (21, 121); and a drive arrangement (64, 164) configured to simultaneously rotate said filter assembly (18, 118) about said central axis and displace said backwash arm (54 a, 54 b, 154 a, 154 b) so that said suction nozzle (58, 158) moves through a range of radial positions on said filter disk, thereby causing said suction nozzle to follow a spiral tracking motion across a surface of said filter disk. a backwash arm (54 a, 54 b, 154 a, 154 b) extending between adjacent of said plurality of filter disks, said backwash arm terminating in a suction head (56 a, 56 b, 156 a, 156 b) comprising a suction nozzle (58, 158) in facing relation to one of said first and second filter screens (21, 121) and said suction head further comprising at least one rotatable roller (62, 162) deployed to provide rolling contact with said one of said first and second filter screens; a pivot arrangement (60, 160) for accommodating motion of said backwash arm so as to bring said suction nozzle (58, 158) into close contact with said one of said first and second filter screens (21, 121); and a drive arrangement (64, 164) configured to simultaneously rotate said filter assembly (18, 118) about said central axis and displace said backwash arm (54 a, 54 b, 154 a, 154 b) so that said suction nozzle (58, 158) moves through a range of radial positions on said filter disk, thereby causing said suction nozzle to follow a spiral tracking motion across a surface of said filter disk.