  The work is devoted to the investigation of physical nature of H-bond. The
H-bond potential $\Phi_{H} (r,\Omega)$ is studied as an irreducible part of the
interaction energy of water molecules. It is defined as a difference between
generalized Stillinger-David potential and the sum of dispersive and multipole
interaction potentials. Relative contribution of $\Phi_{H} (r,\Omega)$ to
intermolecular potential does not exceed (10\div15)%.
