Well heck, we may never know for sure what causes the flash rust. Until recently, I was one of those guys who stated that hot water will absolutely cause rusting, but with so many guys reporting just the opposite, it seems to be a hit-or-miss, some do, some don't, kinda thing.
Like I said before, I have high iron content from my well, but use no water softener. When I had my water tested years ago, it did seem like there was a certain amount of alkalinity, but nothing close to the unsafe limit. Now I wonder if too much "base" can cause the rust, like mild bleach :hmm: . Ok, I'm overthinking this :surrender: .
I do wish I had an old barrel I could experiment on. I'd like to try disstilled water versus my well water, to see if the rust is the same. I'm certainly not going to experiment on my good barrels. Oh well, I guess we just do what works for us. Bill