Originally Posted by chumpsteak
5.0 to 5.2 is low for mash pH, anywhere from 5.2 to 5.7 is fine, but the ideal range after 15 minutes is 5.3 to 5.6 roughly. Tons of info on water in the brew science forum.
That water report looks really good. Very soft water like you said. I would be mostly concerned about any amount of chlorine or chloramines in the tap water. If your bottled water batch turns out good you can probably get by with using a chloramine tablet in your tap water and your beers will turn out great. IMO chlorine and chloramines cause chlorophenols which cause a range of off flavors and weirdness.
The ph listed in the water report the OP attached is 6.7-9.8 which is pretty high IMO. My concern was that the grain bills are not bringing the ph down to a more adequate range and is remaining high during the mash although I could be wrong.
When the OP brewed with bottled water his mash ph read 5.0 which, yes is a little low but that is not with his city water supply.
As far as tannin extraction it is my understanding that this is only a concern if too hot a water (over 170) is used to sparge in conjunction with a high ph. If the sparge water is is within proper range tannin extraction is not a concern.
I admit I am not the most water chemistry intelligent brewer so I will defer to those more in tune that chime in