I'm a newbee to the aquarium hobby, so take my information with a grain of salt...
My tap water is low pH and very soft, so I tried using bottled water instead (from the 1 gallon jugs). I didn't realize that I was using "distilled" water from Poland Spring for my water changes/refills.
Anyway, there is no negative effect on my tank so far. Basically, I've found that the bottled water in general has a higher pH and is harder than my tap water.
The difference I've found between "regular" and "distilled" bottled water was that distilled (87.5 ppm) was slightly harder than regular (52.5 ppm).
Can anyone else provide more concrete facts about this?