I've got an ultrasonic humidifier. I found that running it for a few hours with Brita filtered water made my whole room full of white dust. So I started using only distilled water. Since getting distilled water means I have to walk a few blocks and refill a 10 liter container every two days, I'll probably not buy an ultrasonic humidifier in the future.

I have both a humidifier and purifier working 24/7, several meters apart and I've noticed that tap water in any form does make the purifier work harder, but demineralized doesn't.

Makes me glad that I got an evaporative one then. At the time I was mostly thinking that the ultrasonic one would bother my dog.