4-Amino-pyridinium 4-amino-benzene-sulfonate 4-ammonio-benzene-sulfonate monohydrate.

The asymmetric unit of the title compound, C(5)H(7)N(2) (+)·C(6)H(6)NO(3)S(-)·C(6)H(7)NO(3)S·H(2)O, contains one 4-ammonio-benzene-sulfonate zwitterion ((+)H(3)NC(6)H(4)SO(3) (-)), one 4-amino-benzene-sulfonate anion (H(2)NC(6)H(4)SO(3) (-)), one 4-amino-pyridinium cation and two half-mol-ecules of water, each lying on a twofold rotation axis. The various ions and molecules in the structure are linked through N-H⋯O, N-H⋯N and N-H⋯S hydrogen bonds and C-H-π inter-actions into a three-dimensional framework.