The invention is directed to an improved desalination process to produce potable
water. The process represents an improvement of hybrid of membrane and desalination
technologies. The improvement of the invention comprises the operation of an ion
selective membrane at a variable pressure as a function of the cost of electricity
to form a softened salt water that is blended in variable proportions, to increase
the top operating temperature of the desalination system and increase recovery
of potable water, with untreated salt water.