Multipole electrostatic moment analysis of the cavity-water interfacial potential reveals that there is a potential shift of -3.96 Volt from the liquid water bulk phase to the cavity center, which is primarily attributed to the water molecular Bethe potential (quadrupole) contribution. Since the current work focuses on the excess free energy for the solute ion pair (in which case the interfacial potential contributions cancel exactly), the Bethe potential for liquid NaCl is not discussed further here.