In the title compound, C8H10N2O4·H2O, the imidazole N atom is protonated and one of the carboxylate groups is deprotoned, forming a zwitterion. An intramolecular O—H⋯O hydrogen bond occurs. The crystal structure is stabilized by intermolecular N—H⋯O and O—H⋯O hydrogen bonds. In addition, intermolecular N—H⋯O and O—H⋯O hydrogen bonds link the molecules into two-dimensional networks parallel to (10).