The structure of the title compound, catena-poly[[cadmium(II)-di-μ-chlorido-μ-(1,4-diazoniabicyclo[2.2.2]octane-1-carboxylato)] [[aquachloridocadmium(II)]-di-μ-chlorido] dihydrate], {[Cd(C₈H₁₅N₂O₂)Cl₂][CdCl₃(H₂O)]·2H₂O}n, contains two kinds of independent one-dimensional chain, viz. {[Cd(C₈H₁₅N₂O₂)Cl₂]⁺}n and {[CdCl₃(H₂O)]⁻}n, and uncoordinated water molecules. Each CdII cation in the {[Cd(C₈H₁₅N₂O₂)Cl₂]⁺}n chain is octahedrally coordinated by two pairs of bridging chloride ligands and two O atoms from different bridging carboxylate groups. CdII cations in the {[CdCl₃(H₂O)]⁻}n chain are also octahedrally surrounded by four bridging chloride ligands, one terminal chloride ligand and one coordinated water molecule. Hydrogen bonds between solvent water molecules and these two independent chains generate a three-dimensional framework containing two-dimensional zigzag layers.