In the title compound, C16H14N4O4S center dot H2O, the benzene and pyridine rings make a dihedral angle of 85.8 (1)degrees. Both enantiomers of the chiral title compound are statistically disordered over the same position in the unit cell. The methyl and carbonyl group attached to the stereogenic center (C-5 of the thiazolidine ring) were therefore refined with common site-occupation factors of 0.531 (9) and 0.469 (9), respectively, for each stereoisomer. In the crystal, intermolecular N-H center dot center dot center dot O, O-H center dot center dot center dot O and O-H center dot center dot center dot N hydrogen bonds link the molecules, forming a three-dimensional supramolecular network. The crystal structure further shows pi-pi stacking interactions [centroid-centroid distance = 3.5063 (13) angstrom] between the pyridine rings.