catena-Poly[[triaqua-nickel(II)]-μ-5-carb-oxy-benzene-1,3-dicarboxyl-ato-κO:O].

In the title compound, Ni(C(9)H(4)O(6))(H(2)O)(3), the Ni(II) ion has a distorted NiO(5) square-pyramidal geometry, the maximum deviation from the least-squares plane formed by the basal atoms being 0.9351 (13) Å. The basal plane is formed by two O atoms from carboxyl-ate residues of the 5-carb-oxy-benzene-1,3-dicarboxyl-ate ligand and by two O atoms from water mol-ecules. The O atom of the third water mol-ecule is axially positioned, 1.7890 (19) Å perpendicular to the basal plane. The 5-carb-oxy-benzene-1,3-dicarboxyl-ate ligand bridges the metal atoms, forming a polymeric chain along the b axis. O-H⋯O hydrogen bonds between the water mol-ecules and carboxyl-ate groups stabilize the crystal structure.