What causes white dust and how can I prevent it?

White dust is caused by minerals suspended in hard water, not by a defect in the humidifier — the higher the mineral content of your water, the greater the potential for white dust. To reduce it, use distilled water and a Homedics demineralization cartridge in the water tank. The demineralization cartridge should be replaced every 30–40 fillings, or more often if using very hard water. (Page 6, 12)