I bought an RO system from Buckeye Hydro; I'd do it again. Russ was very helpful in getting me what I needed, fittings and so on. I've included a pic of how I do it below.
Here are a couple considerations, depending on how you're going to draw RO water for brewing. I don't have a tank and a faucet, as you can see from the picture. I simply hung my RO filters on the wall next to the sink, and feed them from the faucet, which has a threaded spout.
I run the RO water directly into a 7-gallon Aquatainer. I do this when I'm brewing, so that the water I start with from the Aquatainer (oddly enough, an almost perfect amount when I add 1 gallon of very hard tap water) is replenished by the RO filter. It's just one of the brew-day duties.
Another consideration is capacity. Mine is 50 gallons per day capacity, and it's pretty close to that in output--3-4 hours of running it into the Aquatainer and I have water ready for the next brew day. If I were to do it over again, I'd have bought the 100 GPD filter; it's only a few dollars more and I'd have less wait time. It works great, and I'm happy, but I'd have gone higher capacity.
If you're feeding a tank with an auto shutoff, and the tank has enough capacity for your brew day, then filter throughput is probably not as important and you can save the few bucks.
The three colored lines you see in the pic are the source water (Blue, hooked up to the faucet, which leaks which is why I have the red rag over it); output line (White, going into the Aquatainer; I drilled a 1/4" hole and it fits the tube perfectly); and Yellow, which is the waste water. The waste water just goes down the drain.
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