Actually we are on well water, all of us drink it. I also live at the coast in the Pacific Northwest.
So it's very humid and anything with a surface will grow some kind of spores around here! My jug had been sitting less than 2 days with a cap. I have other jugs of the same type used for different things like the garden and filling my ice maker. Neither of those grow the "mold", so it must be acv related.
So if simply cleaning the jug isn't the solution for me, is it safe to use this method or should I just skip it? We aren't big chemical users since we are also on septic, aside from the toxicity posed by them (ever breath them in or get it on your skin, accidents happen). I do use bleach as needed, but couldn't see doing it that often.