I have high bicarbonate levels in my tap water. So, I carbon filter my tap water (for chlorine) into gallon jugs that I have in my brewroom for brew day. I also have 6x3gallon jugs I fill with RO water from Walmart or other stores nearby. I will use a combination of my filtered tap water and RO water in conjunction with Gypsum and CaCl depending on what I am going to brew - using B'run Water.
To be honest, most of the beers I brew are probably 80-100% RO water - all my light lagers, my APA's, IPA's, Wheats, Bitters,etc.
My Ambers, Scottish, Milds, are generally 60-80% RO.
My Browns, Porters, Stouts are 30-50% RO.