I'll agree on the lower fluoride and chlorine content in RO or distilled water. But there are no such controls on spring water, depends on the water source. And none of these methods produce sterile water, especially spring water. Bottled water is tested only at bottling, while municipal water is monitored multiple times a day. Not starting Internet wars, but not using tap water because it isn't as clean is throwing money at these companies. I'll agree for mineral content or taste reasons.
Health Canada link is better on the eyes than FDA, and I'm Canadian.
http://www.hc-sc.gc.ca/fn-an/securit/facts-faits/faqs_bottle_water-eau_embouteillee-eng.php