This is pretty crappy one-size-fits-all advice in itself.

If you’re willing to use distilled water, ultrasonic humidifiers have their own advantages over evaporative.

I’m personally willing to buy distilled water. It’s a dollar per gallon, and we only need the humidifier during a short few months. You can even buy a small countertop water distiller for under $60.

I'm thoroughly unconvinced.

Doing some basic research... hard water is overwhelmingly various carbonate and bicarbonates of magnesium, calcium, sulfur, iron, maganese, and aluminum. All of which are essential nutrients and readily soluable in water.

The other proposed problem was pathogen aerosols- however I was unable to access anything but an abstract. So, I don't know if they survived being aerosolized, produced more and/or worse pathogen count than evaporative humidifiers, Nor the size of the pathogens.

It seems to me the known risk is mostly mechanical (Asthma, exacerbated COPD, etc) and nonpersistent (particles dissolve and are used or excreted via the same pathways as when consumed). With an unknown risk on the pathogen side.

> If you’re willing to use distilled water, ultrasonic humidifiers have their own advantages over evaporative.

Unless you are anally retentive about cleaning it, ultrasonic humidifiers vaporize microbes into the air. There have been loads of studies about this.

The only real way to avoid this is to use the humidifiers that are boiling the water.