I'm not a food chemist, but I think the answer to your questions
is that any normal water you choose to use in a pizza dough will
not have a level of acidity (low pH) that will adversely affect
the fermentation process or the taste of a crust made from the
dough--or your health. A pH of 5 is not high. A pH of 0 would
be. Remember that acids are always being produced in a dough
during fermentation as long as there is sufficient residual
sugar to keep the fermentation process going. That process
produces acidic by-products (carbonic, lactic, acetic,
propionic, etc.) which are a major factor in lowering the pH in
the dough. Doughs formed by using natural starters (e.g.,
sourdough starters) are loaded with acids--far higher than with
normal doughs. Even at that, they are unlikely to ever approach
a pH of 0 because of the buffering provided by the flour and
other added ingredients. At the 0 level, if you could ever get
there, I suspect the product would be so unpalatable as to be
inedible. Your water has a pH that