Another thing about putting in a R.O. system if your water comes from a well. If your water, as Jeff puts it, is crap (like mine also is, 400 grains of hardness in my raw water and a vein of black manganese in my well) you will probably need a water softener ahead of the R.O so you don't plug up the membrane and shorten its useful life. If it is a municipal water supply, you are probably OK since many municipalities soften their water supplies. You can get that information from the local municipal water works.
I have an R.O. here and can use it to fill jugs for brewing, but rather than taxing our drinking water supply here and encountering the wrath of she who must be obeyed :-), I go to a water softener store, like Culligan or Clearwater and buy 5 gallon jugs of my R.O. brewing water. It costs me only $1.50 to fill a 5 gallon jug and after filling 10, I get a free one. Plus, I can get 15 gallons (enough for a 11 gallon batch) in a few minutes instead of taking a day or two to fill the jugs here at home even though I have a 7.5 gallon reservoir on my R.O. Full disclosure, I just bought a new water softener to replace the one that was about 25 years old and it came with a new R.O. unit as a part of the package. The one I have in operation is the exact same model, is only 4 years old, and is working great so I have a new one in the box that I can part with if anyone is interested. PM me and we can discuss it. I do not work for a store that sells water softeners or R.O units.
Just another thing to consider.