I've run my own water through the gf's BV, no issues at all.
Tossed whatever water was inside, dried it out with a paper towel (following her process), poured in about 300ml of the arrowhead bottle she brought me from her work, brought it to 203F, made myself a pourover, then, while still warm, I took off the lid and walla.. spots on the bottom! I also noticed quite a bit of lint and fuzz from the paper towel I *think*, hrrrm, the water even had an almost... gelatinous consistency. It wasn't as liquidy as one would expect water to be. I tossed the water, and at the bottom, gray-witish deposit spots (not black though), and even got the brown stain as the last of the water evaporated!
Pulled out my test kit, GH took 15 drops, and KH took 14 drops. Test kit instructions go to 12 drops, each drop is 17.9 units.
Moral of this story, don't grow fish in the arrowhead bottled water that my gf's workplace orders, unless you want three-eyed sea monkeys.
Final test, I'll have her brew with baby water next week.