Ordinary tap water is full of lime, calcium and a host ofother minerals. When this water is vaporized, ‘white dust’ can form – a kindof residue buildup that can develop on your walls, floors and furniture. TheVornado Mineral Cartridge is specifically designed for use in your VornadoUltrasonic Humidifier to help filter out the minerals that cause this dust toform. The cartridge contains a specially designed blend of water softeningminerals, reducing lime and calcium buildup. Completely odorless, this filterscrubs your water clean, extending the life of your humidifier. This MineralCartridge, part number MD1-0018, works with models Ultra1, Ultra2 and Ultra3.From the Manufacturer IMPORTANT INTERNATIONAL DISCLAIMER: This item is builtto meet U.S. voltage requirements and may not function properly when used inconjunction with external devices that alter or convert voltage or frequencyof electricity. Improper use or shipping the product outside the U.S. willvoid all warranties.