I use a cheap so-called crappy large Vicks humidifier/steamer the one with the night-light and use regular tap water and add a tablespoon of salt (really kicks up the steaming process, and also; salt is a natural cleanser) + I add Vicks 'menthol' vapor liquid (Swans is cheaper, half the price) although I much prefer to use eucalyptus oil but it's expensive.
Surprisingly the cheap Vicks humidifier/steamer usually last me at least 10 years (more or less), the one I have now works as good as new, but I look after it, keep it clean.
Seriously: it sure is a little noisy
but because I've got it steaming like a wild fog machine in overdrive due to the addition of salt I only need to have it on for 30 minutes, if I leave it on for more than and hour I'll be needing a raincoat! Anyway, I asked the doctor about the addition of salt and they said that's cool!
I also have my own brew of air-freshener that contains; water, 91% alcohol isopropyl, menthol and eucalyptus oil, mixed ingredients well and used in a spray bottle (always shake before use). It's fantastic; just a few sprays around the room will clear the sinuses and it also adds moisture. In Australia I use to buy a can of Parrot Eucalyptus (aerosol) but cannot get it in the US that's why I roll my own.
Anyway; To be safe I don't place the humidifier near electrical appliances and never leave it unattended. Being doing this for years and never had any issues. I always rinse out the unit regularly and because of the salt the unit does not build up mold.