The organic anion of the title compound, {[Na(C(15)H(9)O(10)S)(H(2)O)(2)]·H(2)O}(n) {systematic name: poly[[diaqua-[μ-2-(3,4-dihy-droxy-phen-yl)-3,5,7-trihy-droxy-4-oxo-4H-chromene-8-sulfon-ato]-sodium] monohydrate]}, has a nearly planar structure. The Na atom is six-coordinated by O atoms, two from water mol-ecules and four from the anion. The dihedral angle between the ring systems in the anion is 10.1 (1)°. Intra-molecular O-H⋯S and O-H⋯O inter-actions occur. In the crystal structure, an extensive network of classical inter-molecular O-H⋯S and O-H⋯O hydrogen bonds forms layers along the c axis.