Abstract: Reverse osmosis (RO) systems having efficiency enhancing features are disclosed. Included are RO systems having a RO module and a pumping system. A feed fluid line can introduce feed fluid into the pumping system, and the pumping system can increase the pressure of the feed and pass the pressurized feed to the RO module. Such RO systems can also have a recycle stream leading from a concentrate side of the RO module to the pumping system and a purified stream leading from a purified side of the RO module. In some cases, the pumping system can boost the pressure of both the feed fluid and the recycle stream, and the boosted fluids can be fed into the RO module. The pumping system can have first and second pumping chambers for the feed fluid and the recycled concentrate. These pumping chambers can be separate pumps, or they can be referred to as a single pumping system, for example a double-acting simplex plunger pump.