The limescale filter cartridge, specially designed by Laurastar Swiss engineers, allows you to filter tap water before it is used for ironing. By preventing limescale, they ensure a longer life cycle for your iron. They also prevent salt to improve steam quality. Anti-corrosive, they also prevent damage to boiler components. The limescale filter cartridge should be replaced when anti-scale granules turn completely brown. Please note that the water tank holder is required to use this filter.