A flocculation, sedimentation, dehydration or retention composition comprising a stable dispersion of about 10 to 50% concentration by weight of a polymeric Mannich base in a mixture of water, a water-insoluble liquid and an emulsifier all present as a water-in-oil emulsion, the Mannich base comprising an NH-active polymer carrying carbonamide groups at least about 10% of which carry radicals of a reaction therewith of formaldehyde and a primary or secondary alkyl- or hydroxyalkyl-amine wherein the alkyl groups have up to about 18 carbon atoms, and a stabilizing amount of a water-soluble salt of a mono- or multivalent amine, alone or in admixture with a mono- or multivalent amine or ammonia, or of an ammonium salt of a mineral acid and ammonia, or of a carboxylic acid amide. The amine of the Mannich base is preferably dimethylamine or diethylamine and is used in approximately the same molar amount as the formaldehyde. The polymer preferably comprises acrylamide units and the polymerization may be effected either before or after reaction with the formaldehyde and amine.