Abstract: The present invention relates to a non-agglomerating, readily separable mixed bed ion exchange system comprising: (a) a strong base quaternary ammonium anion exchange resin wherein said anion exchange resin has been pretreated with 10 to 800 milligrams of water-soluble sulfonated poly(vinylaromatic)polyelectrolyte per liter of anion exchange resin; wherein the number average molecular weight of the sulfonated poly(vinylaromatic)polyelectrolyte is from 5,000 to 1,000,000; and (b) a strong acid sulfonated cation exchange resin wherein said cation exchange resin has been pretreated with 10 to 800 milligrams of a water soluble cationic polyelectrolyte selected from the group of polymers consisting of poly(vinylaromatic)quaternary amine salts, poly(vinylaromatic)tertiary amine acid salts, or poly(vinylpyridines) acid salts, wherein the number average molecular weight of said polymers is from 5,000 to 1,000,000.