A) acrylic and methacrylic homo- and copolymers, and salts thereof, for example products commercially marketed under the trade names VERSICOL??? E or K by ALLIED COLLOID, ULTRAHOLD??? by BASF, acrylic acid and acrylamide copolymers sold in their sodium salt form under the trade names RETEN??? 421, 423 or 425 by HERCULES, and polyhydroxycarboxylic acids sodium salts.