just for ref:
Permeate: The output from the reverse osmosis membrane (the cleaned water)
Brine: The waste water output from the membrane
Brine ratio: The amount of brine compared to the amount of permeate during operation. To enable a membrane to work properly and live a long life, most of the supply water is allowed to flow across the membrane and exit out through a restrictor. This restrictor keeps some back pressure on the membrane surface.
Most membrane manufactures require a brine ratio of 3:1 to 4:1
Rejection ratio: Ratio of the measured TDS of the membrane inlet water compared to the membrane permeate outlet. Most membranes will have a listed rejection ratio of 95-98%. However, this is
highly dependent on inlet pressure, inlet water temperature and pressure differential across the membrane. This is what determines when a membrane should be replaced.
If you have a brand new membrane that has a rejection ratio of 95% and your supply water has a TDS of 100ppm, the output from the membrane under ideal conditions will be 5ppm
That same system with a supply water TDS of 1000ppm will have an output of 50ppm.
To get rid of what the membrane cant, we use a "DI" (demineralization by ionization) stage, sometimes called "deionization". They are little beads that swap one ion for another, typically hydrogen for whatever the leftover bad ion is. (I'm not a chemist so I may be over simplifying it but you get the idea) These beads are typically a "consumable" product and must be replaced.
for ref, my setup:
HTH's
Av