not shown in fig1 that are housed within a water cylinder 200 as will be further described below the hydraulic output of each hydraulic pump 12 causes the piston rod 14 to move due to the mechanical coupling the movement of the piston rod 14 causes the two dual action pistons to move in unison with the movement of the piston rod 14 the piston rod 14 and the two dual action pistons may collectively be referred to as a reciprocating assembly for clarity this disclosure will describe the features of a single pump and reciprocating assembly but it is understood that this similarly describes the features of all the hydraulic pumps and reciprocating assemblies in the system a source of feed water 110 which includes sources of sea water brackish water and the like is connected to and supplies feed water to the water cylinder 200 by feed water supply lines 254 256 indicated as the long dashed line in fig1 the system 10 also includes high pressure feed water supply lines 262 264 to direct a high pressure feed water from the water cylinder 200 to the ro membrane unit 216 indicated as the thick solid line in fig1 the ro membrane unit 216 produces a volume of permeate that is desalted water which is directed by the permeate line 217 for the desired uses of the desalinated filtrate product the ro membrane.