A third monoclinic polymorph of 3,4,5-trihy-droxy-benzoic acid monohydrate.

The title compound, C(7)H(6)O(5)·H(2)O, is a new polymorph of the structures reported by Jiang et al. (2000 ▶) [Acta Cryst. C56, 594-595] and Okabe et al. (2001 ▶) [Acta Cryst. E57, o764-o766]. The gallic acid mol-ecule is essentially planar (r.m.s. deviation = 0.550†à ). An intra-molecular O-H⋯O hydrogen bond occurs in the gallic acid mol-ecule, which is linked to the water mol-ecule by a further O-H⋯O hydrogen bond. In the crystal, the components are linked by O-H⋯O hydrogen bonds. The hydrogen-bonding pattern differs from those reported for the previous polymorphs.