The crystal studied of the title compound, C(7)H(9)N(2)O(4) (+)·ClO(4) (-)·C(7)H(8)N(2)O(4)·H(2)O, was found to be a racemic twin with a 0.72 (18):0.28 (18) domain ratio. The hydrazidium group is close to planar, with an r.m.s deviation of 0.105 Å; the hydrazide group deviates more from planarity, with an r.m.s deviation of 0.174 Å. In the crystal, the hydrazidium cation, hydrazide mol-ecule, perchlorate anions and water mol-ecules are linked through O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds into a three-dimensional supra-molecular network. In addition, the benzene rings of the hydrazidium and hydrazide units are connected via π-π inter-actions into infinite chains along the c axis; the centroid-centroid distances are 3.486 (3) and 3.559 (3) Å.