I betcha a lot of the minerals precipitate out after the boil.
I use the water that comes out of the spring up on the hill behind my house Unfiltered, untreated. No idea what the ph is like, but it makes tasty beer.
If you use bottled water, get spring water, not something that has been reverse osmosised. That filtering will strip out all the minerals you need for happy beer.
The biggest concern for me when brewing with city water is the chlorine and floride and all the crap they add to it. I guess a lot of that boils off...
Oh don't give me none more of that Old Janx Spirit
No, don't you give me none more of that Old Janx Spirit
For my head will fly, my tongue will lie, my eyes will fry and I may die
Won't you pour me one more of that sinful Old Janx Spirit