In the title compound, {[Co(C10H8O6)(C16H20N4)(H2O)2]·5H2O}n, octahedrally coordinated CoII ions on crystallographic inversion centres are bound by trans O atoms belonging to two hydroquinone-O,O′-diacetate (hqda) anions {systematic name: 2,2′-[(1,4-phenylene)bis(oxy)]diacetate}, two trans-pyridine N-donor atoms from two bis(pyridin-4-ylmethyl)piperazine (4-bpmp) ligands, and two trans aqua ligands. The exobidentate hqda and 4-bpmp ligands form [Co(hqda)(4-bpmp)(H2O)2]n coordination polymer layers parallel to (110) that are anchored into the full crystal structure by O—H⋯O hydrogen bonding between aqua ligands and ligated hqda O atoms. Disordered water molecules of crystallization occupy incipient channels along [100]. However, these could not modeled reliably and so they were treated with SQUEEZE in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155]; the crystal data take the presence of these molecules into account. The crystal under investigation was twinned by non-merohedry, the twin fraction of the components being 53.3% and 46.7%. Only data from the major twin component were used in the refinement.