NEW YORK (Reuters Health) - Bottled water is not necessarily healthier or safer than tap water, Tampa, Florida-based sports nutritionist Cynthia Sass told the American College of Sports Medicine 11th annual Health & Fitness Summit in Dallas.

Twenty-five percent of all bottled water is actually repackaged tap water, according to Sass.

"Bottled water doesn't deserve the nutritional halo that most people give it for being pure," she says. "If you're not an exclusive bottled water drinker, you may find it worthwhile to check into filtering your tap water to save money."

In a recent Gallop survey, most consumers said they drink bottled water because they perceive it to be purer than tap water. Taste and convenience are also factors.

Because bottled water is considered a food, it is regulated by the US Food and Drug Administration. Tap water is regulated by the U.S. Environmental Protection Agency. Both types of water are subject to testing for contaminates.

But Sass points out that an estimated 60 to 70 percent of all bottled water in the U.S. is packaged and sold within the same state, which exempts it from FDA regulation. And 1 in 5 states do not regulate that bottled water.

Moreover, tests on 1,000 bottles of 103 different brands of bottled water found man-made chemicals, bacteria and arsenic in 22 percent of the bottles.

Tap water is also not immune to contamination problems. While most cities meet the standards for tap water, some tap water in the 19 U.S. cities tested was found to contain arsenic, lead, and pesticides, Sass told the conference.

While most healthy adults can tolerate exposure to trace amounts of these contaminates, some people, such as cancer patients undergoing chemotherapy, individuals who are HIV positive or recovering from a transplant or major surgery, pregnant women, children, and the elderly, are more vulnerable.

For these individuals, Sass favors bottled water treated with reverse osmosis, distilled water or city tap water with a filtering system certified by the National Sanitation Foundation.

As for the fitness water craze, skip it, Sass says, noting that fitness and specialty waters with not give an athlete an advantage or edge. In fact, vitamin-fortified waters may pose a risk for over-supplementation.

"Think of your one-a-day vitamin," says Sass. "Some of these waters are multi-vitamins in a bottle, so read the label and compare with the rest of your daily intake, including food," she advises.