The asymmetric unit of the title compound, (C6H20N3)[BiCl6]·H2O, consists of a triprotonated bis(3-azaniumylpropyl)azanium cation, two halves of an octahedral [BiCl6]3− anion, each of the BiIII atoms lying on an inversion centre, and a water molecule. In the crystal, the anions and water molecules are linked by O—H⋯Cl hydrogen bonds, forming chains running parallel to [0-11]. The anionic chains and the cations are further linked into a three-dimensional network by N—H⋯Cl and N—H⋯O hydrogen-bond interactions.