Dr. Jane Sadler, family medicine physician on the medical staff at Baylor Medical Center at Garland, Texas, said bottled water is regulated by the FDA, but when it never leaves the state where it is packaged and sold, which is the case with about 60 percent of bottled water, it becomes exempt from FDA oversight.

"There is no guarantee that bottled water is any better than tap water. Twenty-five percent of bottled water is actually just repackaged tap water," Sadler said in a statement.

"In fact, it's been shown some bottled waters do not meet U.S. Environmental Protection Agency standards so you really have to be careful in your selection of bottled waters. Be sure that you're getting water that's been distilled or that's been processed through reverse osmosis."

Some experts say tap water -- highly regulated by the EPA -- is generally safe, Sadler said.