2-Amino-4-methyl-pyridinium 3-carb-oxy-4-hy-droxy-benzene-sulfonate monohydrate.

In the crystal structure of the title salt, C(6)H(9)N(2) (+)·C(7)H(5)O(6)S(-)·H(2)O, the water mol-ecule acts as an acceptor of bifurcated N-H⋯O hydrogen bonds from the pyridinium H atom and one H atom of the 2-amino group, forming an R(2) (1)(6) ring. The 3-carb-oxy-4-hy-droxy-benzene-sulfonate anions self-assemble via O-H⋯O hydrogen bonds, leading to supra-molecular chains along the a axis. These chains and R(2) (1)(6) motifs are linked via O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds, forming a layer parallel to the ac plane. There is also an intra-molecular O-H⋯O hydrogen bond in the 3-carb-oxy-4-hy-droxy-benzene-sulfonate anion, generating an S(6) ring motif.