Each of the carboxyl-ate -CO(2) fragments of the dianion ligand in the title compound, {[Sr(C(9)H(4)N(2)O(4))(H(2)O)(2)]·H(2)O}(n), chelates to a Sr(II) atom and at the same time, one of the two O atoms coordinates to a third Sr(II) atom. The μ(4)-bridging mode of the dianion generates a square-grid layer motif; adjacent layers are connected by O-H⋯O, O-H⋯N and N-H⋯O hydrogen bonds, forming a three-dimensional network. The eight-coordinate Sr atom exists in a distorted square-anti-prismatic geometry. The crystal studied was a non-merohedral twin with a minor twin component of 24%.