In a previous report, a new model for the thermodynamic description of a fluid/liquid interface was developed. In that model the dual meaning of the interfacial tension as the free energy per unit area of interface, as well as the force per unit length required to increase the interfacial area, is fully exploited. According to that formalism the interfacial tension is the macroscopic observable of the potential energy accumulated within the interfacial layers; it results from the existence of elastic fields occurring in each bulk phase near the interfacial boundary. Here that theoretical framework is used to estimate the width of an air/water interface. The present analysis starts from a novel interpretation of the isothermal changes that are required to occur upon a homogeneous water phase so that its chemical potential could be equal to that of the molecules at the interface. As intuitively expected, this results indicate that the interface is slightly more dense than the adjacent bulk. This difference in density is attributed to minor changes in the spatial distribution of the molecules.