In the title compound, C(10)H(8)N(2)O(10)·2H(2)O, the skeleton of the dicarboxylic acid mol-ecule is approximately planar, the largest deviation being 0.477 (1) Å for an O atom of a nitro group; this nitro group is twisted out of the plane of the ring by 24.6 (1)°. Adjacent mol-ecules are linked by O-H⋯O hydrogen bonds, which connect the dicarboxylic acid and water mol-ecules into a three-dimensional supra-molecular network.