We have hard water and clean our coffee pot about every 6 months or else we sit waiting like anxious puppy dogs as our coffee trickles through, LOL. I think if mold would kill us we'd be dead 3 times now. Mild exposure to molds tweak our immune systems in a good way so that they're primed to fight real illness (full disclosure, I have a molecular biology degree, took a full quarter of immunology and feel what I'm saying is based on real science!).
Which reminds me...one of my guest professors told us about the "fecal veneer". The earth is covered in what amounts to a think layer of feces. We can never get away from germs. Our immune systems like this "friendly reminder" of the bad guys out there.
https://www.thecut.com/2015/05/not-j...p-covered.html
It's a paradox, but people who live in "too clean" of a world are more prone to things like allergy and immune diseases. Of course, there are extremes.