A case of humidifier lung; the key diagnosis is detailed medical history taking
pmc.ncbi.nlm.nih.gov
pmc.ncbi.nlm.nih.gov
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.
In the distillation process, steam from boiling water is condensed which cools it from a hot gas back into a very mineral-free liquid distilled water which collects in a very clean reciever.
Distilled water will evaporate without leaving a trace, unlike most drinking water. More delicious if you ask me.
The dissolved minerals do not evaporate so they are left behind in the boiling vessel. Toxic minerals or not, sodium, calcium, lead, whatever, that's what the solid "scale" left over consists of. This is the traditional physical separation procedure to produce greatly purified water.
But distillation is not perfect, things that are not like minerals can be present in the feed, and if the impurities are things that can evaporate, they will distill in the same way the water does and so not be left behind in the boiling vessel. Basically these are considered Volatile Organic Compounds, things like paint solvents or alcohol themselves are distilled similarly (in industrial quantities before sale) and then they don't leave any residue when they evaporate during use either.
Volatiles if present can sometimes can be reduced by distillation if a certain percentage of water vapor is allowed to escape after it first gets boiling, taking some volatile impurities with it without being collected into liquid form, only letting cleaner water vapors be hitting the condensor later. Some PFAS are like this and anything volatile in significant amounts still may not be acceptable after distillation alone, so to remove these further treatment would be needed like carbon filtration before and/or after a distillation step.
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.