The versatile C15H20N8O6 ligand is coordinated through four of its N atoms to the Cu-II atom in a double-deprotonated tetradentate fashion to give the title complex, aqua[1,3-propanediyldiimino-kappa(2)N-bis(1,3 dimethyl-5-nitroso-2,4(1H,3H)-pyrimidinedionato-kappa(2)N(5),N-6)(2-)] copper(II) monohydrate, [CU(C15H18N8O6)(H2O)].H2O. A water molecule occupies the axial position of the distorted square-pyramidal coordination environment of the Cu atom.