I'm with PCDuck, I got the 5-stage from bulkreefsupply.com and couldn't be happier. I later added a second membrane to up the output and cut down on the waste, it kicks out around 6 gallons an hour of 0ppm water. I've had it for 3 or 4 months and use around 30-40 gallons a week I would say, and the tds meter on it is still reading 0ppm so the filters are still good. A replacement pack of filters with the DI resin is $32, pretty cheap.