5-6 gallons wasted for 1 gallon of RO is certainly nothing to scoff at. So basically for a 5 gallon brew session using pure RO water (no tapwater mix) You're looking at about 50-60 gallons for 9-10 gallons. Wow, it certainly something to keep in mind.Just a quick heads up about RO. RO is great... I have one.. but I also sell them at work... and they use a TON of water. Most systems are about 5 or 6 to 1 for input vs output. Meaning to make 1 gallon of RO water, it goes through about 4-5 gallons of tap water. So, just be prepared to hear that residula going down the drain when its filling the tank. You cant go too much wrong with a Watts system, but other great ones out there are Cuno/Aquapure as well as Everpure. These are mostly higher end, showroom grade RO systems but they perform well. My work is not the place to buy "inexpensive (but good)" RO systems. jd3's suggestions about collecting the waste water is an excellent idea though to comabt what I said above.