Liquid treatment device, comprising: a liquid treatment container containing at least one liquid treatment medium; and a device head adapted for coupling to the liquid treatment container, the device head comprising: • a processing unit; • a memory unit communicatively connected to the processing unit; • means for determining a parameter characterizing the liquid treatment process; • a plug-in module interface for communicatively coupling a plug-in module to the processing unit, configured to enable a communication with different types of plug-in module, wherein the types of plug-in module are distinguished by using different communication standards or by having different functionalities; and • means for mechanically coupling the liquid treatment device to the plug-in module, wherein the device head further comprises a housing part in which at least the plug-in module interface is arranged, which housing part includes the means for mechanically coupling the liquid treatment device to the plug-in module and is configured to fit to a housing part of the plug-in module in a sealing manner to form a closed housing protecting electronic parts of both the device head and the plug-in module from moisture, dust, dirt or mechanical damage, characterised in that the device head comprises: means for identifying the plug-in module; means for loading instructions from the memory unit for the processing unit to handle the parameter according to the connected plug-in module, wherein the instructions are loaded in response to identifying the plug-in module, and wherein the loaded instructions depend on the type of the coupled plug-in module; and means for sending the parameter according to the instructions via the plug-in module interface to the plug-in module. a device head adapted for coupling to the liquid treatment container, the device head comprising: • a processing unit; • a memory unit communicatively connected to the processing unit; • means for determining a parameter characterizing the liquid treatment process; • a plug-in module interface for communicatively coupling a plug-in module to the processing unit, configured to enable a communication with different types of plug-in module, wherein the types of plug-in module are distinguished by using different communication standards or by having different functionalities; and • means for mechanically coupling the liquid treatment device to the plug-in module, wherein the device head further comprises a housing part in which at least the plug-in module interface is arranged, which housing part includes the means for mechanically coupling the liquid treatment device to the plug-in module and is configured to fit to a housing part of the plug-in module in a sealing manner to form a closed housing protecting electronic parts of both the device head and the plug-in module from moisture, dust, dirt or mechanical damage, characterised in that • a processing unit; • a memory unit communicatively connected to the processing unit; • means for determining a parameter characterizing the liquid treatment process; • a plug-in module interface for communicatively coupling a plug-in module to the processing unit, configured to enable a communication with different types of plug-in module, wherein the types of plug-in module are distinguished by using different communication standards or by having different functionalities; and • means for mechanically coupling the liquid treatment device to the plug-in module, wherein the device head further comprises a housing part in which at least the plug-in module interface is arranged, which housing part includes the means for mechanically coupling the liquid treatment device to the plug-in module and is configured to fit to a housing part of the plug-in module in a sealing manner to form a closed housing protecting electronic parts of both the device head and the plug-in module from moisture, dust, dirt or mechanical damage, characterised in that the device head comprises: means for identifying the plug-in module; means for loading instructions from the memory unit for the processing unit to handle the parameter according to the connected plug-in module, wherein the instructions are loaded in response to identifying the plug-in module, and wherein the loaded instructions depend on the type of the coupled plug-in module; and means for sending the parameter according to the instructions via the plug-in module interface to the plug-in module. means for identifying the plug-in module; means for loading instructions from the memory unit for the processing unit to handle the parameter according to the connected plug-in module, wherein the instructions are loaded in response to identifying the plug-in module, and wherein the loaded instructions depend on the type of the coupled plug-in module; and means for sending the parameter according to the instructions via the plug-in module interface to the plug-in module.