In the title compound, C(15)H(14)N(2)O(3)·H(2)O [systematic name: 3-(7-meth-oxy-9H-pyrido[3,4-b]indol-1-yl)propanoic acid monohydrate], the fused rings make dhedral angles of 0.4 (1), 1.1 (2) and 1.4 (2)°. In the crystal, the water mol-ecule is involved in the formation of three independent hydrogen-bonded chains via O-H⋯O and N-H⋯O hydrogen bonds, while the carb-oxy group forms an inter-molecular O-H⋯N hydrogen bond.