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WALNUT CREEK, Calif. - Few plastic water bottles make it into Mary Wilstorn's curbside recycable container - the Concord, Calif., resident buys one plastic bottled water a week and simply refills it from the tap.

"I don't buy bottled water for the so-called 'mountain spring' water," she says. "Tap water is fine by me. And if it came packaged to go, I wouldn't need to use a plastic bottle at all."

It seems like an ideal balance: Plastic bottles afford convenience at a time when the emphasis is on hydrating with water instead of sugary drinks; reusing the bottles helps address environmental concerns over pollution, overflowing landfills and crude oil use from plastic production.

But is the practice healthy?

Some reports suggest reused plastic bottles may break down and leach chemicals into the water. Tests on reused plastic bottles also have detected nasty bacteria.

The information is confusing, and in some cases, flat-out misleading. And ultimately, striking a balance between convenience, the environment and health hinges on drawing your own conclusions.

Why not just uncap a new plastic water bottle? Isn't bottled water better than tap?

Not necessarily.

The Environmental Protection Agency strictly regulates all public water; the Food and Drug Administration oversees the bottled water industry with less stringent regulations. Until recently, few bottled water manufacturers publicly revealed their water sources. Turns out about 40 percent of bottled water is really filtered tap water.

Plastic also takes a toll on the environment, partly because it is a byproduct of petroleum refining. The Earth Policy Institute notes that more than 10 million barrels of crude oil are used each year to make the plastic water bottles. And the National Resources Defense Council reports that an estimated 9,700 tons of carbon dioxide are emitted annually to transport bottled water overseas to California.

The sheer numbers don't stop there. In 2006, 28.3 billion gallons of bottled water were sold in the United States, according to a report by Beverage Marketing Corp. About 86 percent of those bottles were thrown away, not recycled - alarming to environmentalists because a buried water bottle takes up to 1,000 years to biodegrade, says the Container Recycling Institute.

Rumors and e-mail warnings have sent up red flags about reusing plastic bottles. But are they true?

* Claim: A University of Idaho student's masters thesis found that reused plastic water bottles leach chemicals.

Reality: Not true, says the FDA. The student's tests were not subjected to peer or FDA review. The FDA has classified polyethylene terephthalate (PET) - the material used in most disposable water bottles - as meeting federal standards for food-contact materials.

* Claim: The plasticiser DEHA is a human carcinogen that can leach from the plastic bottles into the water, possibly causing cancer.

Reality: First, the plasticizer used in PET is diethlhexyladipate, not diethylhydroxylamine (DEHA). The American Cancer Society states, "The U.S. Environmental Protection Agency says DEHA 'cannot reasonably be anticipated to cause cancer … or other serious or irreversible chronic health effects."

* Claim: Freezing water releases dioxins in plastic bottles.

Reality: Plastics contain no dioxins, says Rolf Halden, assistant professor in the Department of Environment Health Sciences and the Center for Water and Health at Johns Hopkins. "Freezing actually works against the release of chemicals," he adds. "Chemicals do not diffuse as readily in cold temperatures, which would limit chemical release if there were dioxins in plastic, and we don't think there are."

* Claim: A University of Calgary study found coliform (typically from fecal matter) and heterotrophic (bacteria from the mouth) in 12 percent of 75 water bottles reused by elementary school children.

Reality: Yes, bacteria was present, but the study's author concluded that a lack of personal hygiene was to blame. The bottles and kids' hands were not properly cleaned before refilling.

* Claim: It's dangerous to drink water from a plastic bottle left in a hot car.

Reality: True, and the same goes for exposing an open water bottle to room temperature for too long, says Keith Christman, senior director of packaging for the American Chemistry Council's Plastics Division. "You want to treat it as an opened food product container," he says. "That's why many food products say 'refrigerate after use' because bacteria can grow in warm conditions."

* Claim: Lexan is a polycarbonate plastic, used in sports bottles such as Nalgene, that contains bisphenol A (BPA), which if consumed can cause chromosomal disruption, miscarriages, birth defects and obesity.

Reality: It depends on whom you ask. The Environment California Research & Policy Center notes that more than 130 studies found BPA at very low doses was linked to adverse health effects. Also, 38 leading scientific experts on BPA have called for more research because of those studies.

Proponents argue that the research is inconsistent and based on animal studies. Also, regulatory agencies, such as the FDA and European Union's Scientific Committee on Food, consider plastic safe for reuse.

The UC Berkeley Wellness Letter, compiled by 14 faculty members, offers insight for both perspectives. "No human health risk has been established," it writes, "but there have been concerns because traces of BPA have been detected in human urine samples."

So, are plastic bottles safe to use repeatedly?

Where Nagalene bottles are concerned, any amount of BPA leached is probably miniscule, says John Swartzberg, Clinical Professor of Medicine at UC Berkeley and chair of the Wellness Letter's editorial board.

"Of course, you don't want to put anything in your body that you don't have to," Swartzberg says. "Most times, any leaching would happen with the first few uses, so just wash the bottle out."

The bigger health issue stems from bacteria in reused bottles: Proper cleaning is essential.

"Saliva gets into the bottle and if there's enough warmth, it can grow," Swartzberg said. "Conceivably it can cause disease. To our knowledge, there's been no outbreak of disease from unclean bottles, but that's no reason to contaminate yourself."

Bottles should be cleaned using hot, soapy water. Avoid using dishwashers because high heat can cause degradation, Swartzberg said.

Swartzberg suggests using a scrubber designed for baby bottles to thoroughly clean the inside, neck and lip of the bottle. Then let the bottle air dry completely before refilling.

Finally, check the bottle for visible thinning or cracking because damaged areas can harbor bacteria. Disposable plastic bottles are not designed for multiple use so they are susceptible to breaking down over time.

"Plastic is not really the issue," Christman said. "Bad hygiene and improper cleaning are the main reasons why reusing a bottle can have health risks. Obviously, single-use bottles are more sanitary. Really, it comes down to a consumer's personal choice."

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