Chemistry of the 

Keep in mind:

The EPA regulates public drinking water (tap water), whereas the FDA regulates bottled water. However, bottles sold interstate does not require any regulation at all.This means that bottle companies that receive their water from a spring within a certain state can sell it back to that same state without the FDA having to check anything; this means that they could put any sort of chemical in the bottles with it going un-noticed. Though tap water has several chemicals in it as well, they are regulated by the EPA to a minimal consumption level so that they are virtually harmless to the consumers.At the same time, remember that bottles sold interstate can have quantities of chemicals in them that can actually be damaging healthwise to the consumer population. Bottled water tend to have several chemicals, such as turbitidy, phthalates, radioactive elements, arsenic, barium, sodium, inorganic and organic bacterias, and much more - Tap water have some of these too, but in a much safer and harmless quantity! Not to mention that most plastic bottles contain BPA, a chemical toxic to both humans and living organisms in the ocean! You can interpret that these bottles are also not recycled (America has a 30% recycling rate for bottles), so the majority of the plastic is left in the ocean. This has huge negative environmental impacts. That's why tap water is definitely the BETTER choice!