The title compound, C₁₇H₁₅NO₄·H₂O, derived from DL-tyrosine crystallizes as an unusual hydrogen-bonded acid-monohydrate dimer. The asymmetric unit contains two organic molecules and two water molecules. Dimers link through (aryl)O-H...O=C hydrogen bonds along the [101] direction, forming a one-dimensional chain of rings, and further associated via inversion centres (forming a chain of rings aligned in the opposite direction) generating columns. Ruffled sheets arise from interlocking of isoindole rings via π-π(arene) stacking and C-H...π(arene) interactions; C-H...O interactions generate a three-dimensional network.