In the title compound, 2Na(+)·C(6)H(4)O(9)S(2) (2-)·2H(2)O, the benzene rings of the 4,5,6-trihy-droxy-benzene-1,3-disulfonate ions, which are stacked parallel to each other forming rods parallel to the a axis, are slightly deformed (planarity, symmetry) mainly because of the high degree of substitution. The two sodium ions, located within pockets of the anion rods, are coordinated by six and s...