Good clarification Andy - the reverse osmosis membrane is the only part of the typical system that has water loss, all the others are throughput filters/resins where you get out (in terms of water volume!) is what you put in.
Bob/Blown - I am curious about the "zero waste" setups. The only thing I can imagine is some sort of loop system where the "reject" water (carrying a higher concentration of contaminants than the original input) is fed back through the RO membrane and partially diluted with some "fresh" water to make up volume/flow. While more efficient in terms of water use, I can't see this working too well in terms of water purity... you would jack up the concentration of contaminants in the retentate so high the rejection rate of the membrane would start to suffer and you dump it all on the DI resin. I must be missing something here... sorry for the digression