As you can see from the previous posters, the idea of the best brewing water changes depending on the brewer. For all beers, there needs to be some minerals in the water. Buying RO or distilled water gets you a blank slate and you can add the desired minerals when you brew. Water from areas next to the mountains often is quite soft as the water doesn't spend much time in the aquifer absorbing the minerals. Some aquifers have more soluble minerals, some have different compositions. Where I live I had a choice of 3 aquifers when my well was drilled and I'm quite sure each was of different mineral composition. I happened to choose the best water in the nation for brewing the beers I like.