Results of modification of composite membranes intended for desalination of sea and surface water are presented. It has been shown that modifying the selective layer of the sea water desalination membranes can stabilize the membrane rejection in the case of an increase in the feed water temperature to 40A degrees C. The modification of the membrane for surface water desalination makes it possible to increase silicon rejection to a level of 99.78% at 35A degrees C. The new line of membrane elements with a modified composite membrane by RM Nanotekh is intended for application at desalination plants in hot regions (up to 40A degrees C) in the first place, as well as in water treatment units at thermal power plants and regional power stations operating at a high temperature of feed water (up to 35 degrees).