Often, bottled water is tap water. It may be run through an additional filtration system, or have some flavor added to distinguish itself, but its still mostly tap water. It will still have all the chemicals added to tap water because these are required by the FDA. The big difference is, you don't have to pour it. It comes in a convenient plastic bottle that is destined to head to a landfill, where it will stay for the next 2000 years before it completely breaks down.
I do not think that bottled water is better for anybody's health than tap water. I think that tap water in most cities can be very safe. But it also depends on the location of the tap water. I think that while bottled water can be very convenient, they do not have any benefits healthwise over tap water.
I don't believe there is any evidence that bottled water is better for you. In fact, various consumer associations have done tests on this and found that tap water is perfectly safe to drink, and that some bottled water in fact contains more bacteria and impurities than regular tap water.
If you are in a developed country like the United States or Australia, you do not need bottled water. Study after study has proved this to be true. Tap water is just as clean as bottled water in almost every case, and even won some of the taste tests administered.