In the title hydrate, C12H10N2O4·H2O, the dihedral angle between the benzene and pyrazine rings is 37.70 (10)°. In the crystal, molecules are connected by hydrogen bonds (N—H...O, O—H...O and O—H...O) to generate (1-10) sheets. Aromatic π–π stacking [centroid–centroid separation = 3.7070 (13) Å] links the sheets into a three-dimensional network.
