The title hydrated quinoline derivative, C(11)H(9)NO(3)·2H(2)O, crystallizes as a zwitterion in which the quinoline N atom is protonated. The quinoline ring is essentially planar, with a maximum deviation of 0.017 (2) Å. An intra-molecular N-H⋯O hydrogen bond between the protonated N atom and the O atom of the carboxyl-ate group in the zwitterion forms an S(5) ring motif. In the crystal, the zwitterions are connected into inversion dimers via pairs of N-H⋯O and C-H⋯O hydrogen bonds with R(2) (2)(4) and R(1) (2)(6) motifs. The water mol-ecules are connected via O-H⋯O hydrogen bonds, forming supra-molecular chains along the c axis. Furthermore, the chains and the dimers are connected via O-H⋯O hydrogen bonds, forming ladder-like supra-molecular ribbons along the c axis.