The structure of the title compound, [Cu(PTA)(4)]Cl·6H(2)O (PTA is 1,3,5-triaza-7-phosphaadamantane, C(6)H(12)N(3)P), is composed of discrete monomeric [Cu(PTA)(4)](+) cations, chloride anions and uncoordinated water mol-ecules. The Cu(I) atom exhibits tetra-hedral coordination geometry, involving four symmetry-equivalent P-bound PTA ligands. The structure is extended to a regular three-dimensional supra-molecular framework via numerous equivalent O-H⋯N hydrogen bonds between all solvent water mol-ecules (six per cation) and all PTA N atoms, thus simultaneously bridging each [Cu(PTA)(4)](+) cation with 12 neighbouring units in multiple directions. The study also shows that PTA can be a convenient ligand in crystal engineering for the construction of supra-molecular architectures.