The title compound, {[Cd3(C6H13N2)2Cl8]·2H2O}n, consists of pendant protonated cationic diamine ligands bonded to an anionic one-dimensional coordination polymer chloridocadmate scaffold. Each coordination chain features two kinds of CdII centre, each with distorted octahedral coordination geometry. One CdII cation lies on a centre of inversion and is coordinated by six bridging chloride ligands, while the other is coordinated by four bridging chloride ligands, one terminal chloride ligand and a 1-aza-4-azoniabicyclo[2.2.2]octane aza N atom. This gives a reversible corner-sharing half-cubic linear polymer that lies along the crystallographic a direction. The chains interact through hydrogen bonding with solvent water, with each water molecule accepting one N—H...O interaction from a cation and donating to two O—H...Cl interactions with anionic chains, thus linking three separate chains and completing the packing structure.