The inner salt 4-carboxy-2-(pyridinium-4-yl)-1H-imidazole-5-carboxylate monohydrate

In the title compound, C 10 H 7 N 3 O 4 ·H 2 O, one carboxyl group is deprotonated and the pyridyl group is protonated. The inner salt molecule has a planar structure, apart from the carboxylic acid group, which is tilted from the imidazole plane by a small dihedral angle of 7.3 (3)°.