I think that's the primary point, Wdi. From my understanding on what I've read about the use of Aquafina is that the levels of dissolved solids in it render it essentially "lab-grade" even though it's not marketed that way, obviously.
I've been using it since Fremer (like him or not...) first started talking about it and find it works every bit as well as the more pricey stuff I had been using. It's readily available and cheap.
I've been a tad skeptical about generic grocery-store "distilled" water.