In the anion of the title salt hydrate, H5N2+·C7H5N2O4−·2H2O, the carboxylate and nitro groups lie out of the plane of the benzene ring to which they are bound [dihedral angles = 18.80 (10) and 8.04 (9)°, respectively], and as these groups are conrotatory, the dihedral angle between them is 26.73 (15)°. An intramolecular amino-N—H...O(carboxylate) hydrogen bond is noted. The main feature of the crystal packing is the formation of a supramolecular chain along thebaxis, with a zigzag topology, sustained by charge-assisted water-O—H...O(carboxylate) hydrogen bonds and comprising alternating twelve-membered {...OCO...HOH}2and eight-membered {...O...HOH}2synthons. Each ammonium-N—H atom forms a charge-assisted hydrogen bond to a water molecule and, in addition, one of these forms a hydrogen bond with a nitro-O atom. The amine-N—H atoms form hydrogen bonds to carboxylate-O and water-O atoms, and the amine N atom accepts a hydrogen bond from an amino-H atom. The hydrogen bonds lead to a three-dimensional architecture. An analysis of the Hirshfeld surface highlights the major contribution of O...H/H...O hydrogen bonding to the overall surface,i.e. 46.8%, compared with H...H contacts (32.4%).