We have demonstrated above a novel statistical approach to model and understand the excess thermodynamic functions i.e. (ln γ ± , osmotic coefficient, ϕ, and water activity, a w ) of 135 electrolytes. The basis of our coarse-grained approach is a generalized multipole expansion which describes the interaction of the charges outside a purely statistical, stoichiometrically defined observation volume with the potential originating from the charge distribution inside. Even for the most complex studied electrolyte solutions, the 3rd order expansion, including dipole, quadrupole and octupole contributions, is found sufficient to describe the full set of thermodynamic properties in the whole solubility range. This is a substantial simplification compared to existing heuristic descriptions.