An external chemical dosing system arranged to be located external to an appliance having a plurality of water inlets (29, 30, 31), the system comprising: a plurality of flow sensors each arranged to be located external to an appliance and to be associated with a respective water inlet of the appliance (29, 30, 31), each flow sensor being arranged to determine when water is being supplied through a respective inlet (29, 30, 31); at least one meter (37, 38, 39) arranged to be located external to the appliance and arranged to determine the volume of water supplied to the appliance through one or more of the inlets (29, 30, 31), or the rate at which water is being supplied to the appliance through one or more of the water inlets (29, 30, 31); a pump or valve arranged to be located external to the appliance for dispensing a volume of chemical to the appliance; and a control unit arranged to be located external to the appliance, characterised in that the control unit is arranged to receive signals from each of the flow sensors and the at least one meter (37, 38, 39) and to determine from said signals (34, 35, 36) the stage in a cycle the appliance is at, by determining through which inlets (29, 30, 31) water is being drawn into the appliance, control the pump or valve in dependence on the stage of the cycle the appliance is at, to cause the pump or valve to dispense a chemical to the appliance appropriate for the stage of the cycle the appliance is at; and to control the quantity of chemical dispensed in dependence on the signal, or signals, received from the at least one meter (37, 38, 39), indicative of the volume of water drawn into the appliance at that stage of the cycle. a plurality of flow sensors each arranged to be located external to an appliance and to be associated with a respective water inlet of the appliance (29, 30, 31), each flow sensor being arranged to determine when water is being supplied through a respective inlet (29, 30, 31); at least one meter (37, 38, 39) arranged to be located external to the appliance and arranged to determine the volume of water supplied to the appliance through one or more of the inlets (29, 30, 31), or the rate at which water is being supplied to the appliance through one or more of the water inlets (29, 30, 31); a pump or valve arranged to be located external to the appliance for dispensing a volume of chemical to the appliance; and a control unit arranged to be located external to the appliance, characterised in that the control unit is arranged to receive signals from each of the flow sensors and the at least one meter (37, 38, 39) and to determine from said signals (34, 35, 36) the stage in a cycle the appliance is at, by determining through which inlets (29, 30, 31) water is being drawn into the appliance, control the pump or valve in dependence on the stage of the cycle the appliance is at, to cause the pump or valve to dispense a chemical to the appliance appropriate for the stage of the cycle the appliance is at; and to control the quantity of chemical dispensed in dependence on the signal, or signals, received from the at least one meter (37, 38, 39), indicative of the volume of water drawn into the appliance at that stage of the cycle.