The invention relates to water-soluble copolymers used as water retention agents, stabilizers and rheology modifiers in aqueous building material systems based on hydraulic binders such as cement, lime, plaster, anhydrite etc. and in water-based paint and coating systems. The inventive copolymers are highly effective water retention agents even when used in relatively small amounts. They also exhibit excellent air pore stability and adhesiveness. They can also be used as stabilizers in building material and paint systems.