4-Nitro­anilinium 3-carb­oxy-4-hy­droxy­benzene­sulfonate monohydrate

In the title hydrated salt, C(6)H(7)N(2)O(2) (+)·C(7)H(5)O(6)S(−)·H(2)O, the benzene ring of the cation makes a dihedral angle of 1.32 (19)° with the attached nitro group. In the anion, an intra­molecular O—H⋯O hydrogen bond with an S(6) ring motif is formed between the carb­oxyl and hy­droxy groups; the dihedral angle between the carb­oxyl group and the benzene ring is 8.76 (8)°. The crystal structure exhibits inter­molecular N—H⋯O, O—H⋯O, C—H⋯O, and π–π [centroid–centroid distances = 3.6634 (9) and 3.7426 (9) Å] inter­actions to form a three-dimensional network.