From the Office of Dr. Pettey:

Bottled or Tap?

Do you regularly drink bottled water because you think it is safer or healthier for you? When it comes to the health of your teeth, tap water may be better. The reason is that most bottled water does not contain fluoride, unless the label specifically states "fluoride added".

Cavities used to be a fact of life. But over the past few decades, tooth decay has been reduced dramatically. The key reason is fluoride. Fluoride is like vitamins for our teeth. Research has shown that fluoride reduces cavities in both children and adults. For our climate, the water should be fluoridated at about 0.7-0.8 ppm (parts per million). You can call your utility district and ask for the fluoridation rate in your area. If your tap water is not adequately fluoridated, or you typically drink nonfluoridated bottled water, then you can discuss your options with the dentist.