Revrerse Osmosis is a separation process in which feedwater permeates a selective membrane. Dissolved as well as undissolved materials are rejected by the membrane and carried away in the waste (concentrate) stream. The permeate, or product water, contains only a fraction of these materials, with TDS - total dissolved solids (a measure of the salt content in water) only present at a nominal 2-6% of the original feedwater concentration. There are two membrane styles: Cellulose Acetate and Polyamide. Cellulose Acetate (CA) RO Membrane