[grishka]

Water particles produced by an ultrasonic humidifier are larger than those of real steam. I know it because I have one and if I run it for long enough, everything gets covered in a nasty white residue, probably salts from the water. Real evaporation doesn't do that.

[ponyboy123]

I think the difference is that evaporation creates water vapor, whereas an ultrasonic dehumidifier is creating water droplets, some of which are very small, but are still droplets that can carry minerals from the water

[tjmc]

Most datacentres ban the use of ultrasonic humidifiers for exactly this reason.

[jordan_curve]

isn't it generally recommended to use distilled water in these humidifiers for exactly this reason?

[Modified3019]

Yep, both the minerals, and the microorganisms breeding in the water get thrown into the air.

For constant use, I personally recommend "evaporation humidifiers" that use a wick and fan to induce evaporation. The wick will need to be replaced every several weeks.