The structure of the title compound, [La(C5H6O4)(C5H7O4)(H2O)] . H2O, consists of dense layers formed by chains of one-edge-sharing LaO9 (H2O) polyhedra, linked together by the glutarate ligand. The three-dimensional polymeric structure, built up through connection of these layers by the hydrogen glutarate ligand, exhibits cavities accommodating a guest water molecule. The lanthanum ion is tenfold coordinated by four glutarates, acting as bridging-chelating carboxylate groups, by three hydrogen glutarates, three times monodentate, and by one water molecule. Its coordination polyhedron is highly distorted and intermediate between a bicapped dodecahedron and a tetracapped trigonal prism. Hydrogen bonding links the two water molecules and the framework built up from this polynuclear coordination polymer. A very short hydrogen bond, D ... A = 2.484 (3) Angstrom, links the protonated with the deprotonated acid groups in the hydrogen glutarate. [References: 12] 12