Bottled Water testing is through the FDA (Tap water is tested through the EPA.) This different agencies have separate criteria to pass before its okay to consume. EPA makes certain that the results are available to the public (your local government utility should have it posted online for you to view). FDA doesn't require testing but ingredients are needed on the label; ie, spring, well, or tap water and usually salt.
Bottled Water can come from any source, it just needs to be recorded on the label. Unfortunately, the plastic causes endocrine disruption (its the hormone production). Just from the climate change in transport to get the bottled water can freeze/heat the bottle increasing this contamination.
Bottled Water is more expensive than TAP water.