A reverse osmosis system comprising: a plurality of feed pumps (20a-20c) each having a feed pump input and a feed pump output; an input manifold in fluid communication with the feed pump inputs, said input manifold having a first pressure; a membrane feed manifold in fluid communication with the feed pump outputs, said membrane feed manifold having a second pressure greater than the first pressure; a plurality of membrane chambers (12a-12h), each in fluid communication with the membrane feed manifold and generating a permeate output and a brine output, each brine output in fluid communication with a brine manifold; a plurality of booster devices (212a-212b), each having a turbine portion (214a-214b) having a turbine input in fluid communication with the brine manifold and a pump portion (210a-210b) having a booster device pump input and a booster device pump output, each booster device pump output in fluid communication with the membrane feed manifold; a pump input manifold in fluid communication with the booster device pump input; a permeate manifold in fluid communication with each permeate output of the plurality of membrane chambers (12a-12h); a permeate flow meter generating a permeate flow signal; and a medium pressure pump coupled to a motor and variable speed drive, said medium pressure pump communicating fluid from the input manifold to the pump input manifold, said variable speed drive controlling the medium pressure pump to generate a variable third pressure in the pump input manifold greater than the first pressure and less than the second pressure based on the permeate flow signal. a plurality of feed pumps (20a-20c) each having a feed pump input and a feed pump output; an input manifold in fluid communication with the feed pump inputs, said input manifold having a first pressure; a membrane feed manifold in fluid communication with the feed pump outputs, said membrane feed manifold having a second pressure greater than the first pressure; a plurality of membrane chambers (12a-12h), each in fluid communication with the membrane feed manifold and generating a permeate output and a brine output, each brine output in fluid communication with a brine manifold; a plurality of booster devices (212a-212b), each having a turbine portion (214a-214b) having a turbine input in fluid communication with the brine manifold and a pump portion (210a-210b) having a booster device pump input and a booster device pump output, each booster device pump output in fluid communication with the membrane feed manifold; a pump input manifold in fluid communication with the booster device pump input; a permeate manifold in fluid communication with each permeate output of the plurality of membrane chambers (12a-12h); a permeate flow meter generating a permeate flow signal; and a medium pressure pump coupled to a motor and variable speed drive, said medium pressure pump communicating fluid from the input manifold to the pump input manifold, said variable speed drive controlling the medium pressure pump to generate a variable third pressure in the pump input manifold greater than the first pressure and less than the second pressure based on the permeate flow signal.