I've used ultrasonic humidifiers in the past and clean them well enough to avoid humidifier lung, but stopped when I noticed the air quality sensor on my air filter would go nuts when using the humidifier with anything other than distilled water. Which makes sense in hindsight, since any ultrasonic humidifier is essentially blasting everything in the water all over your house. Any contamination in the humidifier or the water is going straight into your lungs.

Steam and evaporative humidifiers have their own downsides, but their respective processes of producing water vapor seem to carry less non-water things with it. Which again makes sense given the physical processes involved.

First, this removes minerals from the water, so the room isn't covered in "white dust" after using the humidifier. But even with this, biofilm can build up inside the machine, which is not visible, but you can touch it. I also remember that when I used just plain tap water, the biofilm built up faster.

This article definitely hit me, I realized that we need to clean the humidifier more often.