In the title compound, {[Co(C8H4O5)(C10H8N2)]·2H2O]} n or {[Co(OH-BDC)(2,2′-bipy)]·2H2O]} n (where OH-H2BDC is 5-hydroxyisophthalic acid and 2,2′-bipy is 2,2′-bipyridine), the Co atoms are chelated by two N atoms from the 2,2′-bipy ligand and by four O atoms from OH-BDC ligands in a highly distorted octahedral geometry. OH-BDC acts as a tetradentate ligand, with one carboxylate group chelating one Co atom and the other binding in a monodentate fashion to two other Co atoms to form a one-dimensional zigzag chain. In the crystal structure, one of the solvent water molecules lies on a crystallographic twofold axis. The one-dimensional molecular chains are assembled into a two-dimensional network via O—H⋯O hydrogen-bonding interactions, while π–π stacking interactions generate a three-dimensional open framework between the two-dimensional networks. [ABSTRACT FROM AUTHOR]