I got rid of all of my ultrasonic humidifiers for this reason. Ultrasonic throws up all sorts of PM2.5 particles which are bad to breathe in. Boiling your water has no such potentially dangerous drawbacks.

Venta humidifiers are a good alternative as well.

Is there risk of parasites too?

FWIW it's not unlikely you'll breathe in some when using normal shower too, but mist certainly more concerning.

>Mist showers would need to use distilled water to prevent lung damage from breathing in hard water minerals.

Unless you have a source for this, it sounds like some strong "programmer medicine".

The lungs have cilia, mucus, and leukocytes that can remove impressive amounts of contaminants (like coal dust or tar from smoking) before it starts becoming a problem, so it's hard to believe hard water mist for less than an hour per day poses any risk. Your showerhead/water being contaminated with Legionella would though.