The El Paso desalination plant is the largest inland plant in the world and uses reverse osmosis to pressurize water to pass through several layers of fine membrane formed by wrapping hundreds of feet around a small inner tube.  There is a lot of energy spent in creating the high pressure system, hence the need for improvements using nanotechnology.  They have 5 pumps currently being used, each with its own section of pressurized membrane bound pipes and the capacity to expand to a 6th pump.   Because the membranes function somewhat slower after several weeks of use, 1 or 2 sections of membranes are offline at a time to remove the biofilm by flushing with water for a week.  Thus, there are always between 1 to 3 of the pumps offline at a time, depending on water usage.  The salt concentrate formed during filtration is collected and piped 22 miles northwest to White Sands where it is gravity feed down into an underground slate bed there, perfect to absorb the salt.  The  El Paso desalination plant can produce up to 27.5 million gallons of of clean permeate water daily.