. The limescale filter cartridge, specially designed by Laurastar Swiss engineers, allows you to filter tap water before it is used for ironing. (Please note that the water tank holder is required to use this cartridge which is already included in SMART systems.). By preventing limescale, it prolongs the life of your iron. By filtering salts, it improves steam quality. Anti-corrosive, it also prevents damage to boiler components. The limescale filter cartridge should be replaced when anti-scale granules turn completely brown. For use with models: Laurastar SMART 1980, SMART U, and SMART I. Can be used with S series models with purchase of a holder for SMART anti-scale cartridges.