Water hardness is caused by a high content of dissolved minerals, especially calcium and magnesium. When such water is heated in a coffee machine, these minerals deposit and form what is known as limescale. These deposits can clog the internal components of the appliance, reduce its efficiency, and negatively affect the taste of the prepared coffee. Filters with this function soften the water, most often using ion-exchange resin. This resin binds calcium and magnesium ions and replaces them with ions that do not form limescale. This protects the coffee machine from damage, extends its lifespan, and contributes to the stable quality of the beverage.