The aromatic rings of the title compound, C(13)H(10)O(3)·H(2)O, are aligned at dihedral angles of 20.6 (1) and 40.8 (1)° with respect to the triangular C(ar-yl)-C(=O)-C(ar-yl) fragment. The hy-droxy groups are each hydrogen-bond donors to separate water mol-ecules, the water mol-ecule itself being hydrogen-bonded to one hy-droxy group and one carbonyl group. The water mol-ecule exists in an unusual four-coordinate environment in the resulting layer structure.