Tap water risk for folks with pulmonary disorders
So I was recently diagnosed with a nontubercular mycobacterial pulmonary infection—it's caused by any of a collection of especially nasty bugs, related to TB but not contagious, and has a long difficult course of treatment with varying degrees of effectiveness. The bacteria that cause these infections are common in soil and water, including tap water. Most people aren't affected by exposure, but people who are immunosuppressed, those using an inhaled steroid, and people with COPD, CF, and other chronic lung conditions are at risk. (I have COPD and use a steroid inhaler.) You can learn more here: https://www.pennmedicine.org/conditions/mycobacterial-lung-disease
I've used tap water in my machine for the past few years, and while nobody has pointed to that as the source of my infection I figure it's the most likely culprit. I still think tap water is probably fine for most people, but if I had known of the risk I would have stuck with distilled.