The asymmetric unit of the title polymeric compound, [Cu(C8H4NO2)(2)(C10H14N2O)(H2O)](n), contains one Cu II atom, one coordinating water molecule, two 4-cyanobenzoate (CB) ligands and one coordinating N,N-diethylnicotinamide (DENA) molecule. The DENA ligand acts as a bis-monodentate ligand, while the CB anions are monodentate. Two O atoms of the CB ligands, one O atom of the water molecule and the pyridine N atom of the DENA ligand form a slightly distorted square-planar arrangement around the Cu II atom which is completed to a square-pyramidal coordination by the apically placed O atom of the DENA ligand, with a Cu-O distance of 2.4303 (15) angstrom. In the two CB anions, the carboxylate groups are twisted relative to the attached benzene rings by 2.19 (12) and 3.87 (15)degrees, while the benzene rings are oriented at a dihedral angle of 5.52 (8)degrees. The DENA ligands bridge adjacent Cu2+ ions, forming polymeric coordination chains running along the b axis. In the crystal, strong water-carboxylate O-H center dot center dot center dot O hydrogen bonds link adjacent chains into layers parallel to (10 (1) over bar) and weak C-H center dot center dot center dot O hydrogen bonds further stabilize the crystal structure. The cyano group C and N atoms of one of the CB ligands are disordered over two sets of sites with equal occupancies.