The short answer
For ultrasonic humidifiers, distilled or demineralized water prevents white dust; evaporative and warm-mist units can use tap water, at the cost of more frequent descaling and wick changes.
What's in tap water
Tap water carries dissolved calcium, magnesium and other minerals; 'hard' water carries more. Boiling or evaporating leaves them behind as scale; ultrasonic misting throws them into the air as white dust.
By humidifier type
| Type | Tap water | Best choice |
|---|---|---|
| Ultrasonic | White dust on surfaces | Distilled or a demineralization cartridge |
| Evaporative | Wick scales sooner | Tap water; replace wicks on schedule |
| Warm mist | Scale in the heating chamber | Tap water; descale weekly |
Alternatives to distilled
- Demineralization cartridges or filters made for your model.
- Reverse-osmosis water from a home RO system.
- Boiled water does not remove minerals; it only kills microbes.
Products mentioned
Questions readers ask
Can I use bottled spring water?
Spring water contains minerals; it's closer to tap water than distilled.
Is white dust harmful?
Health agencies advise avoiding it where possible, especially for people with lung conditions; distilled water prevents it.