It has now been found that superior desalination membranes may be prepared from regular copolyamides having the formula ##STR3## WHERE X IS 2 TO 10, AND PREFERABLY 2 TO 4, Y IS 0 TO 8, PREFERABLY 0 TO 2, R is a divalent aliphatic or aromatic radical having 1 to 34 carbon atoms, and n is not less than 10.