3,3'-Diazenediyldiphthalic acid dihydrate

In the crystal structure of the title compound, C(16)H(10)N(2)O(8)·2H(2)O, the organic mol-ecule is located on a centre of symmetry. The two benzene rings are parallel, but not coplanar, as indicated by N=N-C-C torsion angles involving the azo group of 12.1 (5) and -168.2 (3)°. The organic mol-ecule and the water mol-ecule are linked by O-H⋯O hydrogen bonds, forming a three-dimensional network.