But then, my first reaction would be that there has been no change but mere dissociation leading to a wider distribution of the sodium and chloride ions through

But then, my first reaction would be that there has been no change but mere dissociation leading to a wider distribution of the sodium and chloride ions throughout the water molecules, and therefore it is only a 'physical change'. The less water you use, the closer the sodium and chloride ions get. Until at the end, the sodium and chloride ions have no water molecules at all separating them as they sit neatly in their crystal lattice. <grin>