The asymmetric unit of the title complex salt, (C12H11ClN5)[RuCl4(NO)(C2H6OS)]·H2O, contains a 6-(2-chlorobenzylamino)purinium cation, a tetrachlorido(dimethyl sulfoxide)nitrosylruthenate(III) anion and one solvent water molecule. The RuIII atom is octahedrally coordinated by four Cl atoms in the equatorial plane, and by a dimethyl sulfoxide O atom and a nitrosyl N atom in axial positions. The cation is an N3-protonated N7 tautomer. Intermolecular N–H⋯N hydrogen bonds connect two cations into centrosymmetric dimers, with an N⋯N distance of 2.821 (4) Å. The crystal structure also involves N—H⋯O, N—H⋯Cl and O—H⋯Cl hydrogen bonds.