In the title polymer, [Cd(C5H3N2O2)(NO3)(H2O)]n, the CdII atom is seven-coordinate in a distorted capped octa­hedral geometry by two N atoms of two different pyrimidine dicarboxyl­ate (pmc) ligands, three O atoms from three separate pmc ligands, and two O atoms of disordered nitrate anions or water mol­ecules. The CdII atoms are bridged by the pmc ligands in a chelating/bridging bis-bidentate and chelating bidentate mode, forming sheets parallel to (20-1). The sheets are further linked into a three-dimensional supra­molecular network via classical O—H⋯O hydrogen bonds involving the nitrate anions and coordinating water mol­ecules. Intra­molecular O—H⋯O hydrogen bonding is also observed. The non-coordinating nitrate O atoms are disordered over two sets of sites with occupancies of 0.57 (7) and 0.43 (7).