Optimal structures, interaction energies and harmonic vibrational frequencies of the (H2O)(2)(HX)-H-..., HX = H-2, HF, HC1, FBr, and (H2O)(2)(CIF)-C-... ternary complexes have been determined from the supermolecular MP4 and CCSD(T) calculations with the aug-cc-pVDZ and the aug-cc-pVTZ basis sets. We located three low-energy configurations on the potential energy surface corresponding to H-bonded cyclic complexes and one linear structure in the case of (H2O)(2)(CIF)-C-... and (H2O)(2)(...) H-2. The tunneling motion of the water molecule across the plane of the heavy atom ring was studied. The contribution of the three-body term represents as much as 24% for (H2O)(2)(HBr)-H-... and the smallest value of 5% for (H2O)(2)H-...(2) of the total CCSD(T) interaction energy. The nonadditivity originates mainly from the induction effect. (C) 2003 Elsevier Science B.V. All rights reserved.