The title compound {systematic name: catena-poly[lithium(I)-mu3-acetylsalicylato-hemi-mu2-aqua]}, {[Li(C9H7O4)] x 0.5 H2O}n, is the hemihydrate of the lithium salt of aspirin. The carboxylate groups and water molecules bridge between Li atoms to form a one-dimensional coordination chain composed of two distinct ring types. The water O atom lies on a twofold axis. Hydrogen bonding between water donors and carbonyl acceptors further links the coordination chains to form a sheet structure.