TotalComfort™ demineralization cartridges reduce mineral build-up caused by hard water. Use of high mineral content hard water may cause a white mineral residue to accumulate on surfaces in the room near the humidifier. The mineral residue is commonly called white dust. The higher the mineral content in the water, the greater the potential for white dust. This is not caused by a defect in the humidifier. It is only caused by the minerals suspended in the water. Works with all TotalComfort™ ultrasonic humidifiers 0.5 Gallon and larger. HOMEDICS 4-Pack Replacement Humidifier Filter | UHE-HDC4-6CTM