Connector for placing adjacent devices (2,3) in a head part of a liquid treatment apparatus in liquid communication with each other, wherein the head part devices (2,3) are of the type arranged to receive at least a connecting head of a replaceable liquid treatment cartridge (4,5), wherein a first of the head part devices (2,3) has at least one inlet port, at least one first outlet port (16,17) and at least one second outlet port, wherein, at least in an operational position of the liquid treatment cartridge, only the first of the first and second outlet ports are in liquid communication with at least one of the inlet ports via the liquid treatment cartridge and the second outlet ports are in liquid communication with at least one of the inlet ports (12,13,14), wherein a second of the head part devices (2,3) has at least one first inlet port (19,20), at least one second inlet port and at least one outlet port, wherein, at least in an operational position of the liquid treatment cartridge, only the first of the first and second inlet ports (19,20,21) are in liquid communication with at least one of the outlet ports via the liquid treatment cartridge (4,5) and the second inlet ports are in liquid communication with at least one of the outlet ports, wherein the connector is one of: (i) positionable with respect to the head part devices (2,3) such as to place the first and second outlet ports of the first head part device in sealed liquid communication with the second and first inlet ports of the second head part device, respectively; and (ii) positionable with respect to the head part devices (2,3) such as to place at least the first outlet ports of the first head part device in sealed liquid communication with the first inlet ports of the second head part device, wherein the connector has at least two connector inlet ports (28,29) and at least two connector outlet ports, wherein the connector includes a first flow conductor interconnecting a first sub-set of the connector inlet ports (28,29) and a first sub-set of the connector outlet ports, and wherein the connector includes a second flow conductor interconnecting a second sub-set of the connector inlet ports (28,29) and a second sub-set of the connector outlet ports, and wherein flows of liquid through one of the first and second flow conductors (50,51) are kept separate from those through the other by at least one of the first and second flow conductors (50,51), characterised in that the first and second flow conductors (50,51) are arranged so that the separated flows of liquid cross each other. wherein the head part devices (2,3) are of the type arranged to receive at least a connecting head of a replaceable liquid treatment cartridge (4,5), wherein a first of the head part devices (2,3) has at least one inlet port, at least one first outlet port (16,17) and at least one second outlet port, wherein, at least in an operational position of the liquid treatment cartridge, only the first of the first and second outlet ports are in liquid communication with at least one of the inlet ports via the liquid treatment cartridge and the second outlet ports are in liquid communication with at least one of the inlet ports (12,13,14), wherein a second of the head part devices (2,3) has at least one first inlet port (19,20), at least one second inlet port and at least one outlet port, wherein, at least in an operational position of the liquid treatment cartridge, only the first of the first and second inlet ports (19,20,21) are in liquid communication with at least one of the outlet ports via the liquid treatment cartridge (4,5) and the second inlet ports are in liquid communication with at least one of the outlet ports, wherein the connector is one of: (i) positionable with respect to the head part devices (2,3) such as to place the first and second outlet ports of the first head part device in sealed liquid communication with the second and first inlet ports of the second head part device, respectively; and (ii) positionable with respect to the head part devices (2,3) such as to place at least the first outlet ports of the first head part device in sealed liquid communication with the first inlet ports of the second head part device, wherein the connector has at least two connector inlet ports (28,29) and at least two connector outlet ports, wherein the connector includes a first flow conductor interconnecting a first sub-set of the connector inlet ports (28,29) and a first sub-set of the connector outlet ports, and wherein the connector includes a second flow conductor interconnecting a second sub-set of the connector inlet ports (28,29) and a second sub-set of the connector outlet ports, and wherein flows of liquid through one of the first and second flow conductors (50,51) are kept separate from those through the other by at least one of the first and second flow conductors (50,51), characterised in that the first and second flow conductors (50,51) are arranged so that the separated flows of liquid cross each other.