The Philips WardrobeCare ironing station is equipped with a unique Dual Protect anti-calc system that keeps the device 99% scale-free. The special anti-calc cartridges demineralize the water and also keep it 99% scale-free. Thanks to the Dual Protect anti-calc system, you can use regular tap water when ironing with your WardrobeCare ironing system. The cartridges are very easy to replace. You will know when a change is necessary: the granules in the cartridge change color from blue to brown when they are used up. A package of anti-calc cartridges contains two cartridges. The anti-calc cartridges need to be replaced every 3 to 7 months. Once the granules in the cartridge are completely discolored, it must be replaced.