The invention relates to water-soluble or water-swellable copolymers which contain sulfo groups and which are based on (meth)acrylamide-alkylsulfonic acids and (meth)acrylamide or N-vinyl compounds, and to their use as additives for aqueous construction materials systems or for water-based paint and coating systems. The inventive copolymers also represent water retention agents which are highly effective, even when used in relatively small quantities, and which are highly compatible in construction material and paint systems of this type.