  We apply a phenomenological theory of polar liquids to calculate the
interaction energy between two plane surfaces at nm-distances. We show that
depending on the properties of the surface-liquid interfaces, the interacting
surfaces induce polarization of the liquid in different ways. We find, in full
agreement with available experiments, that if the interfaces are mostly
hydrophobic, then the interaction is attractive and relatively long-ranged
(interaction decay length \lambda\sim1.2\, nm). The water molecules are net
polarized parallel to the surfaces in this case. If the surfaces are mostly
hydrophilic, then the molecules are polarized against the surfaces, and the
interaction becomes repulsive, but at a short-range (\lambda\sim0.2\, nm).
Finally, we predict there exists an intermediate regime, where the surfaces
fail to order the water molecules, the interaction becomes much weaker,
attractive and, at relatively small distances, decays with the inverse square
of the distance between the surfaces.
