How to size an RO system for your feed water.
Match GPD, pressure, and rejection — without over-buying. A short, technical walkthrough from our engineers.
Rated GPD is the membrane's spec at 60 PSI and 77°F. Stabilized GPD is what your system actually produces at your feed pressure and water temperature — usually 30–60% of rated.
If your feed pressure is under 50 PSI, almost certainly. A booster pump brings pressure up to spec and dramatically improves both flow and rejection.
Watch two numbers: rejection (compare TDS in vs. out) and production rate at known pressure. When either drifts off baseline by 10%+, it's time.
For example, if you incoming is 100 and your outgoing is 2, 20 TDS is a sign to change.
Standard RO membranes run a 4:1 waste ratio. Some companies (BRS, Hydrologic, etc...) say their systems can run at 2:1 or 1:1 just because of the membranes they use, which is inaccurate.
Systems cannot run below 3:1 without heavy scaling, costing you more money in membrane replacement.
Systems can run at 2:1 with soft incoming water, but in order for it to run 1:1 without ruining the membrane, recirculation and automated pure water flushes of the membrane are required.