IN THE TITLE COMPOUND [SYSTEMATIC NAME: 5-(5,7-dihydr-oxy-4-oxo-4H-chromen-yl)-2-hydroxy-benzene-sulfonic acid dihydrate], C(15)H(10)O(8)S·2H(2)O, the benzopyran-one ring is not coplanar with the phenyl ring, the dihedral angle between them being 41.35 (3)°. No H atom was placed on the sulphonic acid group because it was not possible to distinguish between the two S=O bonds and the S-O bond. In the crystal, the mol-ecules are linked by classical O-H⋯O and C-H⋯O intra- and inter-molecular hydrogen bonds and aromatic π-π stacking inter-actions [centroid-centroid distance of 3.4523 (14) Å between the 1, 4-pyran-one rings and the benzene rings, and 3.6337 (14) Å between the benzene rings] into a supra-molecular structure.