3-Amino-2-methyl-4-oxo-3,4-dihydro-quinazolin-1-ium p-toluene-sulfonate monohydrate.

In the title hydrated mol-ecular salt, C(9)H(10)N(3)O(+)·C(7)H(7)O(3)S(-)·H(2)O, the cation is protonated at a quinazolinone N atom and an intra-molecular N-H⋯O hydrogen bond occurs. In the crystal structure, inter-molecular N-H⋯O and O-H⋯O hydrogen bonds and C-H⋯O, C-H⋯π and weak aromatic π-π stacking inter-actions [centroid-centroid separations = 3.8648 (12) and 3.9306 (13) Å] help to establish the packing; a short S=O⋯π contact is also seen.