Question:
I bought a Maxxima RO/DI unit. As I wait for it to arrive, I asked theinternet shop I bought it from, "how long are the hoses?" so I can plan inadvance how to get the water from a faucet to the unit to my tank...

The response I got was that the inlet i about 4' long (ok, I can add anextension), the outlet is rigidized 1/4" tubing, NON_PRESSURIZED!!. Said Icould add just extend tge outlet as long as the destination was _downhill_from the unit.

I guess I can make due with a sump below the unit, then pump it into thetank, but SHEESH! The units aren't cheap, you'd think they could throw inan integrated pump or something to help deliver the damn water...

Answer: Reverse osmosis (ok, nanofiltration) works by imposing a pressuredifference across a membrane that is mainly permeable to water. If youput backpressure on the outlet side of the membrane then you decrease thedeltaP across the membrane. That means that the amount of product thatyou get out will decrease.

On paper, it goes to zero when the delta(P) across the membrane equals theosmotic pressure across the membrane. In practice, it significantlyreduces output long before that.

So, unless there is something really flakey about the Kent membraneholder, you will be able to put the output above the level of themembrane, at the cost of reduced output.

They certainly make RO units with a booster pump on the inlet side, andthey are relatively expensive. Of course, if you have a booster pump onthe inlet side, you can run water further uphill on the outlet side, sincethe important variable is delta(P) across the membrane, not the absolutepressures. (Until something breaks.)

I think you got a "cover my ass" response. Either that, or they weretrying to sell you a drinking water kit.

If you have good line pressure, then you should be fine. If you don't,then you are probably going to have problems. FWIW, 10 meters of water =1 bar pressure, more or less. So if the water has to go uphill by 10meters, that will have the same effect as reducing the line pressure tothe unit by one bar, or 14.something psi.