This European Standard specifies definitions, principles of construction (but not dimensions) and design, requirements on performance and operation as well as methods for testing the performance of adjustable chemical dosing systems for conditioning water intended for human consumption inside buildings (see [1]) which are permanently connected to the mains supply. The concentration in the treated water of the active chemical(s) as well as of any other ingredient or minor component (including possible contaminants) should not exceed the parametric values laid down in the existing legislation in the Member States for the water intended for the human consumption, as implemented by the national authorities.