Tap water is fine for everyday use when you are using a cleanable water tub. If you have a standard humidifier tub, we recommend that you use distilled or deionised water. The water should be changed after each use—even if it is not all used within one night. Please do not use any of the following in your humidifier: Bleach, alcohol, chlorine or ammonia-based solutions Moisturising, antibacterial or glycerine based soaps Additives like eucalyptus oil or other scented oils Water softening and unapproved descaling agents These products could damage your humidifier and its function, or leave harmful residual vapours that could be inhaled if not rinsed thoroughly.