Thanks "Shnnn" for the reminder regarding off-gassing the chlorine from the water, as I hadn't thought about this for a long time.
Since I have very hard water, with white scale if left untreated, our tap water is unacceptable. I had originally thought that Distilled Water would be better, but Rowenta warned against that. After having read a little further regarding galvanic corrosion when constructing something using multiple metals, I see why distilled water could be a problem. Not that any of you really want to read this but, I suspect this is why no Distilled Water in their irons: under "Condition 3. The metal junction must be bridged by an electrolyte"
http://www.corrosionist.com/Galvanic_Corrosion.htm
I assume spring water is just someone else's tap water (extra cost to me), not as bad as mine. Yet it would still be a conductor, so not as bad at attacking the seams on the inside of an iron. I suspect this may an issue for leaking irons.
I guess you're right about there being low salt after the softener, but perhaps for the same reason as distilled, the softener has taken too many minerals out & left the water less conductive.
BTW, I have one Teflon-coated iron and really don't prefer it over a smooth stainless steel surface. I am curious if anyone has tried the "quick pass over the wax paper" idea with a hot Teflon iron? Might make is slipperier.