The crystal structure of the title compound, 3Rb+·C6H5O73-·H2O, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The hy-droxy group participates in an intra-molecular hydrogen bond to the deprotonated central carboxyl-ate group with graph-set motif S(5). The water mol-ecule acts as a hydrogen-bond donor to both terminal and central carboxyl-ate O atoms. The three independent rubidium cations are seven-, six- and six-coordinate, with bond-valence sums of 0.84, 1.02, and 0.95, respectively. In the extended structure, their polyhedra share edges and corners to form a three-dimensional network. The hydro-phobic methyl-ene groups occupy channels along the b axis.