The instantaneous charge distribution inside the observation droplet is due to both, ions and water. It can be complex depending on the electrolyte composition and concentration. This distribution generates an electrostatic potential in the environment. The average interaction of this potential with the charge distributions outside the droplet, averaged over all possible configurations explored by the system, determines the interaction energy U de . We choose to describe such an electrostatic potential at a distance, R, outside the droplet as multipole expansion in spherical coordinates. We express this distance, R = n R R h , in units of the hydration radius, R h , of the electrolyte. It is determined by the composition of the solution, its density, and an effective number n h of hydration water that depends on the electrolyte and the expansion order (see Appendix for details). This choice allows us to conveniently express the interactions in terms of a dimensionless distance unit, n R , removing the dependence on concentration and molar volume.