In the zwitterionic mol-ecule of the title compound, C(10)H(7)N(3)O(4)·H(2)O, one carboxyl group is deprotonated and the pyridine N atom is protonated. The pyridinium and imidazole rings form a dihedral angle of 5.23 (1)°. An intramolecular O-H⋯O hydrogen bond occurs. In the crystal, inter-molecular N-H⋯O, O-H⋯N and O-H⋯O hydrogen bonds link the zwitterions and water mol-ecules into sheets parallel to (102).