Since the water has already evaporated, the scale formed is no longer related to the water, and adding a salt water softener will not prevent this, because salt softeners leave sodium in the water, which will also leave water spots. The NaturSoft® Solution Numerous Softener failures / service problems http://griffinotuut.blogzag.com/42689119/whole-house-water-filter-and-water-softener-eine-bersicht