The present form of barium acetate, formulated as [Ba(C₂H₃O₂)₂(H₂O)₃]_n, is the largest reported hydrate of the salt and this leads to a distinct structural behaviour setting it apart from the rest of the family. The compound is a linear polymer with a nine-coordinate Ba(O_aqua)₃(O_acetate)₆ monomer unit. The non-H part of the structure is ordered according to C2/m symmetry, while the disordered water H atoms only abide by this symmetry in a statistical sense. Each molecule is halved by a mirror plane bisecting the Ba centre, one water molecule and one acetate ligand, while containing the other acetate ligand. The chains are interconnected by a disordered water-water/acetate O–H⋯O hydrogen-bonding network involving all water H atoms. The structure and stability of this phase are compared with the other known acetates of barium which differ in the degree of hydration.