2-Hydr-oxy-3-methoxy-benzoic acid monohydrate.

The asymmetric unit of the title compound, C(8)H(8)O(4)·H(2)O, contains two organic mol-ecules which are connected by the two water mol-ecules through O-H⋯O hydrogen bonds, forming an R(4) (4)(12) ring. Further O-H⋯O hydrogen bonds assemble these rings through R(6) (6)(18) rings, giving rise to infinite helical chains arranged around the b axis. These helical chains are assembled by offset π-π stacking inter-actions [centroid-centroid distance = 3.6432†(8)†à ] between the aromatic rings of neigboring chains, forming a supra-molecular network.