Evidence is presented that the interfacial tension or excess free energy per unit area of the planar interface between extensive, rigid, apolar walls and modeled water is an arithmetic sum of three independent quantities: the surface tension of water, the contribution of the integrated wall-water dispersion interaction, and the contribution of the net exclusion volume associated with the rigid, noninteracting wall. The fact that the interfacial tension is linearly dependent on the wall-water interaction parameter is the inspiration for two conjectures: the interfacial water structure is independent of epsilon(SD) and the mean interfacial water density profile is not a measure of the interfacial water structure.