These Air Innovations Humidifier Demineralization Filters are recommended for customers with hard water. Each filter will last up to 90 days depending upon usage and water quality.These powerful hard water filters help prevent white dust from forming in your humidifier by removing calcification and other impurities in the water. These demineralization filters are compatible with most Air Innovations Humidifier models including: MH-408, MH-504,.. See full description for further details