Don't want to hijack the thread but thanks for the tip on this. I went back and reread the thread on hot water heaters. One thing that comes to mind is they advertise some as "glass lined". Not sure what effect that might have on the issue but thought I'd muddy the waters a bit more. Pun intended.
Just out of curiosity I did a taste test between my hot and cold taps. No discernible difference for me. We've been using the hot supply since we started AG with no recognized ill effects in the end products. I think for science we may have to do a double brew day and do one with all cold supply and one with all hot supply. I know my water is fairly hard here as we get precipitate when we boil it. Thanks again @loopie_beer More to think about!