I was curious what municipal pH distribution looks like around the U.S., so I made a quick county-level map. It is not a perfect tap-water map, but it is a useful bit of background texture.
The data comes from the Water Quality Portal. Caveat: those observations can come from rivers, reservoirs, wells, estuaries, and other monitoring sites, not just municipal taps. Some counties are sampled heavily and others barely show up.
For growing, this is just a curiosity map. There is no replacement for measuring your own pH at the tap, in the reservoir, and after nutrients are mixed.