The Co^II cation in poly[[aqua(μ-benzene-1,2-dicarboxylato-κ³O¹,O²:O¹)(μ-4,4′-bipyridine-κ²N:N′)cobalt(II)] trihydrate], {[Co(C₈H₄O₄)(C₁₀H₈N₂)(H₂O)]·3H₂O}_n, is octahedrally coordinated by two N atoms of two 4,4′-bipyridine ligands, three O atoms from phthalate anions and a fourth O atom from a coordinated water molecule. The packing consists of planes of coordination polymers linked by hydrogen bonds mediated by three solvent water molecules; the linkage is achieved by the water molecules forming intricate oligomeric clusters which also involve the O atoms of the phthalate ligands.