In the title hydrate, C19H15N3O3·H2O, the three aromatic groups in the quinoline derivative are close to coplanar: the central oxa-diazole fragment makes dihedral angles of 15.7 (2)° with the benzene ring and 5.30 (14)° with the quinoline ring system. In the crystal, the organic mol-ecules are connected with water mol-ecules by pairs of O-H⋯N hydrogen bonds involving the quinoline and oxa-diazole N atoms. The mol-ecules form stacks along the a axis, neighboring mol-ecules within each stack being related by inversion and the shortest distance between the centroids of the oxa-diazole and pyridine rings being 3.500 (2) Å. Mol-ecules from neighboring stacks are linked by weak C-H⋯O hydrogen bonds, forming a three-dimensional structure.