The thing about distilled water is that it is chemically only water and that is a certainty.
Many of the bottled waters are actually pumped from rivers (like the Monongahela near Pittsburgh) or from underground aquifers that may have been infiltrated by local waste waters. Some are actually taken from the pipes of city water supplies (like Acton Mass).They are then filtered and bottled to sell.
Reverse osmosis is a process for taking water and forcing it through a filter to eliminate chemicals and minerals. There are cities in Florida that get their drinking water by taking in brackish swamp water and pumping it through those filters to make clean RO drinking water.
Source(s):
Look up web sites that talk about the source of the water sold by Pepsi and Coke.