A different and inherently more expensive type of RO system may be needed, depending on whether you can adapt what you have. Nominally, an RO membrane (preceded by some set of filters) will produce filtered water and waste (brine) until the back pressure approaches some fraction of the input pressure. The filtered water would go to a pressure storage tank and thence to the faucet or refrigerator, the brine is dumped into a drain pipe. Unfortunately, this simple description would lead to a brine flow that was always on. Hence the special faucet that controls the input to the RO filter. To get more output pressure and avoid this type of faucet, pumping schemes that lower the pressure on the output of the RO membrane while increasing it into the pressure storage tank are used along with simple controllers. (SpectraPure sells pumps for this purpose.) One type uses the brine pressure itself to drive the pump. For control one also needs pressure sensors, a controller, and a water flow cut-off solenoid. kas

There are several ways that an RO system can be configured, so some of the generalizations above are not truly general. One can simply feed water to an RO membrane (after prefiltering out junk and chlorine with a carbon filter) and send the RO output to a faucet and the waste (brine) to a drain. This is the minimal configuration. The next level of complexity would add a pressure tank to the RO side. This will store RO water, improving flow when needed, but the RO efficiency will drop as the back pressure on the membrane increases. An elaboration that I use, primarily with parts I've purchased from SpectraPure, makes use of a peristaltic pump driven by the waste water. This pump re-establishes the RO water pressure to the tank while effectively lowering it to near zero on the membrane side for efficient filter operation. The pump doesn't use electricity directly, but low-voltage is used by the pressure sensor control of the valve that allows water to the membrane. My house water at this writing is 96 psi and my RO water is at 64 psi. The RO water is plumbed to various places in the house. The RO membranes don't really like 96 psi, so a mechanical pressure limiter is used to set the input at the filters to around 60 psi. Even more elaborate systems can be engineered recirculating the brine and thereby maximizing extraction efficiency. kas Here is a link that might be useful: Spectrapure

Does anybody have a water filtration unit that does "reverse osmosis (RO) combined with a superior carbon filter"? Ive done some research - but would really like to hear from others. Leaning towards RO and carbon based on EWG article (http://www.ewg.org/.../ewgs-water.../filter-technology). I think we would be best suited to something with its own faucet at our sink.

If you do buy an RO system, you might want to check out the Brondell H20 Circle+. It is $370 on Amazon. (I bought our first one for only $300, but the price has gone up since then.) I can't vouch for it 100% yet since it has only been 2 weeks. :-) But I can say that the design is very nice and it is pretty simple to hook up, although we did have to buy a different valve to hook up to the Karbon. The nice thing about this system is the filters and tank are all contained in one unit. (See picture.) It is a much cleaner design than other RO systems, and it looks like changing the filters will be easy. (Or old system was a real pain.) Of course, the filters are not cheap. I have found them at Brookstone for $56, but they are $80+ on amazon. I'm hoping since we will be using 2 systems we don't have to change the filters as often. You might want to do the math and see what is more cost effective.