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Energy-minimization studies of the title compound, C15H13N2O6+.NO3-.H2O, suggest that the stable conformation of the molecule should be that with the carboxyl groups coplanar with the pyridine ring. Isolated in the solid as a pyridinium nitrate monohydrate, the significant rotation of these carboxyl groups from coplanarity with the aromatic ring may be attributed to networks of hydrogen bonding.