The structure of a third pseudopolymorphic hydrate of brucine, brucine-water (1/2) [systematic name: 2,3-dimethoxystrychnidin-10-one-water (1/2)], C23H26N2O4粈2O, has been determined at 130 K. The asymmetric unit comprises two independent brucine molecules and four water molecules of solvation. The four water molecules form uncommon cyclic hydrogen-bonded homomolecular R44(8) tetramer rings, which then form primary hydrogen-bonded chain substructures extending down the 21 screw axis in the unit cell. The two brucine molecules are linked peripherally to these substructures by either single O-H...Nbrucine or asymmetric three-centre O-H...Obrucine hydrogen bonds.