Not really any
Bottled water is watched to make sure there aren't any obvious contaminants (lead, bacteria
, etc) but not really to make sure it's pure or that there aren't trace minerals
, sediment, or even the contents are what they say they are.
It's not a drug, and as such is subject to standards for foods, such as a certain number of bug parts are ok, etc. Bottled water is not much cleaner truthfully than tap.