(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.

(E)-2-{[1-Carb-oxy-2-(1H-indol-3-yl)ethyl-iminio]meth-yl}-6-hy-droxy-phenolate.

In the zwitterionic title compound, C(18)H(16)N(2)O(4), the dihedral angle between the planes of the benzene and indole rings is 26.38 (10)°. An intra-molecular N-H⋯O hydrogen bond generates an S(6) ring motif.