(E)-2-[(2,4-Dihy-droxy-benzyl-idene)aza-nium-yl]-3-(1H-indol-3-yl)propano-ate monohydrate.

In the zwitterionic title compound, C(18)H(16)N(2)O(4)·H(2)O, the dihedral angle between the planes of the benzene and indole rings is 39.20 (8)°. An intra-molecular N-H⋯O hydrogen bond generates an S(6) ring motif. In the crystal, inter-molecular hy-droxy and water O-H⋯O(carboxyl-ate) and N(+)-H⋯O(carboxyl-ate) and indole N-H⋯O(water) hydrogen bonds give a three-dimensional structure.