Our municipal water is absolutely horrible for brewing. I bought the slick and portable HBrewO system at a homebrew conference a number of years ago out of convenience... it and their cartridges are probably more expensive than is justified. But they were there, and I was there, and it's very convenient for me because I don't really have a good set-up for a larger home RO system. I connect it to the hose bib out on my deck, and let 'er fly. The discharge water goes into the back yard to water the grass and plants. I stopped capturing the discharge water for other uses, because it was more trouble than it was worth.
I make 15 or 20 gallons at a time, about once a month. For brewing water, I use between 1/3 and 2/3 of my RO water depending on the beer, and the rest is charcoal-filtered tap water to get rid of the chlorine. What I don't brew with, gets used in the coffee maker, and to replenish my aquariums.