The title compounds, C16H16O5 (I) and C16H16O5·H2O (II), were structurally characterized by single-crystal X-ray diffraction. Compound I crystallizes in monoclinic space group P21/c with a = 10.5574(10), b = 8.3576(9), c = 16.5528(16) , β = 91.762(3)°, Z = 4, R = 0.0524 and wR = 0.1084. The molecules are jointed into a chain by intermolecular O-H···O and C-H···O hydrogen bonds, which form layers parallel to (001). The chains run along the [110] and [110] directions alternatively layer by layer, and are assembled into a network by intermolecular O-H···O (carboxyl) hydrogen bonds. On the other hand, the hydrate complex (II) crystallizes in the triclinic space group P1 with a = 5.1451(2), b = 10.4583(4), c = 14.8267(5) , α = 70.900(2), β = 82.478(2), γ = 81.359(2)°, Z = 2, R = 0.0393 and wR = 0.0983. The molecules are linked into infinite two-dimensional ribbons by O-H···O (carbonyl) and solvent-bridged O-H···O hydrogen bonds.