RO Stage

In a one-stage RO system, the feed water enters the RO system as one stream and exits the RO as either concentrate or permeate water. 

In a two-stage system, the concentrate (or reject) from the first stage then becomes the feed water to the second stage. The permeate water is collected from the first stage is combined with permeate water from the second stage. Additional stages increase the recovery from the system.