The structure of the title compound (common name: amodiaquinium dichloride dihydrate), C20H24ClN3O2 +·2Cl−·2H2O, was previously determined from powder diffraction data [Llinàs et al. (2006). Acta Cryst. E62, o4196-o4199]. It has now been refined from diffractometer data to a significantly higher precision. The dihedral angle between the quinoline and benzene rings is 54.57 (6)°. The central amino N atom interacts more strongly with the quinoline ring than with the benzene ring, as indicated by the shorter C—N bond length [1.341 (2) Å compared to 1.431 (2) Å]. In the crystal, molecules are packed into a three-dimensional network/supramolecular structure through hydrogen bonds between the amodiaquinium cations, chloride anions and water molecules.