The title compound (systematic name: {5-[(7-chloroquinolinium-4-yl)amino]-2-hydroxy­benzyl}dimethylammonium dichloride dihydrate), C20H24ClN3O2+·2Cl−·2H2O, has one amodiaquinium dication, two Cl− anions and two water mol­ecules in the asymmetric unit. The crystal structure was solved by simulated annealing from laboratory X-ray powder diffraction data, with data collected at room temperature. Rietveld refinement of this model led to a final Rwp of 0.047 to 1.79 Å resolution. A three-dimensional network of hydrogen bonding links the amodiaquinium cations via water mol­ecules and Cl− ions.