The reaction of Co(II)(TpivPP) {TpivPP is the dianion of 5,10,15,20-tetra-kis-[2-(2,2-di-methyl-propanamido)-phen-yl]por-ph-yrin} with an excess of KCN salts and an excess of the 18-crown-6 in chloro-benzene leads to the polymeric title compound catena-poly[[dicyanido-2κ(2) C-(1,4,7,10,13,16-hexa-oxa-cyclo-octa-decane-1κ(6) O){μ3-(2α,2β)-5,10,15,20-tetra-kis-[2-(2,2-di-methyl-propanamido)-phen-yl]porphyrinato-1κO (5):2κ(4) N,N',N'',N''':1'κO (15)}cobalt(III)potassium] dihydrate], {[CoK(CN)2(C12H24O6)(C64H64N8O4]·2H2O} n . The Co(III) ion lies on an inversion center, and the asymmetric unit contains one half of a [Co(III)(2α,2β-TpivPP)(CN)2](-) ion complex and one half of a [K(18-C-6](+) counter-ion (18-C-6 is 1,4,7,10,13,16-hexa-oxa-cyclo-octa-deca-ne), where the K(I) ion lies on an inversion center. The Co(III) ion is hexa-coordinated by two C-bonded axial cyanide ligands and the four pyrrole N atoms of the porphyrin ligand. The K(I) ion is chelated by the six O atoms of the 18-crown-6 mol-ecule and is further coordinated by two O atoms of pivalamido groups of the porphyrin ligands, leading to the formation of polymeric chains running along [011]. In the crystal, the polymeric chains and the lattice water mol-ecules are linked by N-H⋯O and O-H⋯N hydrogen bonds, as well as weak C-H⋯O, O-H⋯π and C-H⋯π inter-actions into a three-dimensional supra-molecular architecture.