The title compound, {(C(7)H(15)N(2)Cl)(2)[Cd(3)Cl(10)]·4H(2)O}(n), consists of 1-chloromethyl-1,4-diazoniabicyclo[2.2.2]octane dications, one-dimensional inorganic chains of {[Cd(3)Cl(10)](4-)}(infinity) anions and uncoordinated water molecules. Each of the two independent Cd(II) ions, one with site symmetry 2/m and the other with site symmetry m, is octahedrally coordinated by chloride ions (two with site symmetry m and one with site symmetry 2), giving rise to novel polymeric zigzag chains of corner-sharing Cd-centred octahedra parallel to the c axis. The organic cations, bisected by mirror planes that contain the two N atoms, three methylene C atoms and the Cl atom, are ordered. Hydrogen bonds (O-H...Cl and O-H...O) between the water molecules (both with O atoms in a mirror plane) and the chloride anions of neighbouring chloridocadmate chains form a three-dimensional supramolecular network.