RO/DI performance (GPD etc)

All RO units have a flow restrictor or they would not work, its what creates the backpressure that drives the water through the membrane. Depending on what brand of unit you have its probably a white tube a couple of inches long and maybe 3/4" diameter installed in the waste line, probably with writing like 750mL or something on it. If you don't see anything like that it could be inside the 90 degree fitting on the waste line exiting the membrane housing or even inside the waste tubing as a capillary tube which is the style I prefer since it can be fine tuned for your exact water conditions. If you waste too little the membrane may wear out prematurely and if you waste too much you are wasting water plus reducing the GPD of thetreated water since you are not providing sufficient backpressure. 4:1 is the normal waste ratio and can be timed with a measuring cup and watch or clock.