In the title compound, C(13)H(11)N(3)O(4)·1.5H(2)O, the pyridine ring forms a dihedral angle of 1.50 (6)° with the benzene ring. An intra-molecular O-H⋯N hydrogen bond forms a six-membered ring with an S(6) ring motif. In the crystal structure, one water mol-ecule is disordered over two positions around an inversion centre with site-occupancy factors of 0.5. Inter-molecular O-H⋯N, O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds consolidate the structure into a three dimensional network. A π-π stacking inter-action with a centroid-centroid distance of 3.5949 (7) Å is also present.