A method and system for treating water in order to desalinate the water where the system and method includes a reverse osmosis or distillation unit for producing a first concentrate and at least partially desalinated water. The first concentrate stream is directed to a first demineralization unit which utilizes nanofiltration membranes to treat the first concentrate stream so as to produce a permeate and a second concentrate stream. The second concentrate stream is directed to a second demineralization unit that includes an ion exchange device which in turn treats the second concentrate stream by producing a stream of at least partially demineralized water and third concentrate stream. The stream of at least partially demineralized water is mixed with the stream of at least partially desalinated water produced by the reverse osmosis or distillation unit.