When we bought the house and inherited the SW tank system, it came with an RO (no DI) system under the kitchen sink. It also had a pressure storage tank, which meant you always had a a few gallons of ready made RO water, and a faucet upstairs for household use. And a line ran downstairs to the sump room for the SW tank use.
However, the RO system was not owned, and we had to pay $30+ a month to Canadian Springs to maintain it (change filters, etc). Well, after being on Canreef and searching around on the internet, I soon discovered there was a better way, ie. install and maintain your own.
I bought this used RO/DI from a local Canreefer, and turns out, it is a pretty good system.
http://www.airwaterice.com/product/1...r-100-GPD.html
It is 75 gpd, has an Auto Shut Off valve and I have an inline dual TDS meter giving after RO and after DI readings. It also has a pressure gauge. I retained the pressure storage tank and separate RO only feed for upstairs use and drinking water. Here is a pic of the RO faucet on the kitchen sink.
So I am pretty happy with my RO/DI system.