The title compound, C(11)H(7)NO(4)·H(2)O, contains a 3-carb-oxy-quinolin-1-ium-2-carboxyl-ate (qda) zwitterion and one water mol-ecule. In the crystal, pairs of N-H⋯O hydrogen bonds link the mol-ecules into inversion dimers, and these dimers are further connected by O-H⋯O hydrogen bonds into a three-dimensional supra-molecular architecture. In addition, π-π inter-actions occur between pyridine and benzene rings from different qda ligands [centroid-centroid distance = 3.749 (1) Å] and the dihedral angles of the -CO(2)H and -CO(2) groups to the quinoline system are 8.47 (3) and 88.16 (6)°, respectively.