The title complex, [Ni(C(18)H(18)N(2)O(4))(H(2)O)], lies on a mirror plane with the Ni(II) ion coordinated by two N and two O atoms of a tetra-dentate Schiff base ligand and one water O atom in a distorted square-pyramidal enviroment. The -CH(2)-CH(2)- group of the ligand is disordered equally over two sites about the mirror plane. The dihedral angle between the mean planes of the two symmetry-related chelate rings is 37.16 (6)°. In the crystal structure, inter-molecular O-H⋯O hydrogen bonds link complex mol-ecules into one-dimensional chains along [100] and these chains are linked, in turn, by very weak inter-molecular C-H⋯O hydrogen bonds into a two-dimensional network.