A cartridge for removable connection to a mixing device (49; 60; 75) to form a device for dosing a flowable substance into a liquid includes a housing (13; 37; 71) accommodating a reservoir (14; 38; 72) for holding the flowable substance; an outlet port (15; 42; 73) for connection to an inlet port (16; 95) of the mixing device on connection of the cartridge to the mixing device (49; 60; 75); and a conduit (17) of flexible material, arranged to form at least part of a conduit connecting the reservoir (14; 38; 72) to the outlet port (15; 42; 73). At least a section (39; 74) of the conduit (17) of flexible material is arranged to form part of a peristaltic pump including at least one motor (7); and at least one actuator element (22; 53; 61; 80) with a moveable contact surface, coupled to the at least one motor (7), at least in use, for causing the conduit section (39; 74) to be at least partly compressed at successive locations along its length. At least a part of the conduit (17) of flexible material comprising the conduit section (39; 74) included in the peristaltic pump is mounted to the cartridge, such as to enable a force counteracting a force caused to be exerted by the actuator element(s) (22; 53; 61; 80) on the conduit section (39; 74) included in the peristaltic pump to be exerted on the conduit section (39; 74). The at least one actuator element is journalled on the mixing device (49; 60; 75). The conduit section (39; 74) included in the peristaltic pump is arranged to be compressed by forces exerted by the actuator element(s) (22; 53; 61; 80) only when the cartridge is connected to the mixing device (49; 60; 75).