7‐Hydroxy‐4‐methyl‐2 H ‐chromen‐2‐one monohydrate

In the title compound, C 10 H 8 O 3 ·H 2 O, the 2 H ‐chromen‐2‐one ring system, also known as coumarin, is planar. Intermolecular O—H...O hydrogen bonding between the solvent water molecule, and the carbonyl and hydroxyl groups of the coumarin ring system links the molecules into a two‐dimensional network parallel to the (10) plane. In addition, the crystal packing is stabilized by π–π interaction between the coumarin ring systems of the inversion‐related molecules stacked along the a axis, with a centroid–centroid separation of 3.536 (1) Å.