The Truth About Leaving Bottled Water in a Hot Car

August 21st 2015

If you leave a bottle of water in a hot car, is it safe to drink? Or is it better to toss it? (And by "toss it," we mean recycle the bottle.)

Rumors have been swirling for years that drinking water left in a hot car is unsafe to drink and can even cause breast cancer. As is the case with many public health scares, it can be difficult to discern whether these rumors are overblown exaggerations, or legitimate causes for concern.

I contacted the International Bottled Water Association (IBWA), a collection of U.S. and international bottled water distributors and suppliers for an answer. Christopher Hogan, Vice President of Communications of IBWA, told me via email that, "the claim that bottled water left in a hot car can be dangerous, most often spread by social media channels, such as Facebook messages or via email chains, is untrue."

Hogan pointed out that bottled water is made with PolyEthylene Terephthalate, or PET, plastic, a substance that is approved and regulated by the U.S. Food and Drug Administration (FDA) and used to package other types of food and drink, including peanut butter, juice, beer, and wine.

Researching potential contaminants.

Hogan sent me a statement from the American Cancer Society addressing emails that circulated in 2007. These emails claimed that bottled water left in hot cars may contain diethylhexyl adipate (DEHA), and referred to DEHA as a potential carcinogen.

"These emails are apparently based on a student’s college thesis," According to the American Cancer Society. "In fact, DEHA is not inherent in the plastic used to make these bottles, and even if it was, the US Environmental Protection Agency (EPA) says DEHA 'cannot reasonably be anticipated to cause cancer, teratogenic effects, immunotoxicity, neurotoxicity, gene mutations, liver, kidney, reproductive, or developmental toxicity or other serious or irreversible chronic health effects.’”

A study conducted in 2009 by the Environmental and Water Resources Division of the Indian Institute of Technology Madras found that while trace amounts of DEHA were present in bottled water, regardless of temperature, these levels were within the guidelines established by the World Health Organization for safe drinking water.

Are other compounds harmful?

Other recent studies have focused on other compounds, such as antimony and bisphenol A (BPA): Antimony is a chemical element that can cause respiratory irritation and gastrointestinal problems, and should not be transported with food, according to the Center for Disease Control (CDC); BPA is a chemical component present in polycarbonate plastic, which can be used to make 3- and 5-gallon water bottles, but isn’t present in the PET plastic used to make smaller bottles.

In 2014, Lena Ma and colleagues at the University of Florida conducted a study in China in which they kept 16 brands of bottled water in 158 degrees Fahrenheit for four weeks (considered a “worst case scenario” in terms of the temperature and amount of time the water might be left in a car). Only one of the 16 brands of bottled water tested surpassed the Environmental Protection Agency (EPA) acceptable levels of antimony and BPA.

BPA has become a buzzword in recent years, but exposure to low levels is more common than most people might think. According to the CDC, BPA is present is the urine of “nearly all” of people tested. The CDC notes that the presence of BPA doesn’t necessarily imply negative health effects.

The FDA has approved BPA as safe for the packaging of food and drinks. Packaging containing BPA is marked with a resin code with the number 7. The National Toxicology Program and the FDA are working together to continue to evaluate the safety of ingesting low levels of BPA. In 2012 and 2013, the FDA granted petitions that prohibit the use of “certain BPA-based materials in baby bottles, sippy cups, and infant formula packaging.”

The website recommends limiting exposure to BPA due to the chemical’s “estrogen-like activity,” especially among women who are pregnant, as BPA may effect brain development in the womb.

With regards to antimony, a European study published in 2011 indicated that antimony leaching from PET bottles reaches only 1 percent of the tolerable daily intake recommended by the World Health Organization, even after storage in temperatures of 302 degrees Fahrenheit.

Another study, published in 2008 in the journal Water Research, found that after water bottles were exposed to extreme temperatures “only a small fraction of the antimony in PET plastic bottles is released into the water. Still, the use of alternative types of plastics that do not leach antimony should be considered, especially for climates where exposure to extreme conditions can promote antimony release from PET plastics.”

Is it safe to drink?

I asked Hogan if there are any temperature conditions, or a specific length of time, that would cause the IBWA to view bottled water as unsafe to drink.

Regarding this question, IBWA doesn’t have such a guideline,” Hogan told me. “In general, we don’t recommend storing water for the long term under any adverse conditions, such as exposure to direct sunlight, heat sources, and in areas where volatile chemicals, such as gasoline or cleaning materials, are stored. Another way to look at the question is to ask, ‘How would you store a bottle of juice, soda, or an energy drink?’”

Ma told me that to minimize risk, she would recommend not drinking bottled water left in a car, though she said she’s done it before.

“[Leaving a bottle of water in a car for] just a day or two won’t matter that much,” Ma said. “The problem is accumulative from many years of exposure.”

Researcher Lena Ma said that she would recommend drinking tap water whenever possible. "At home, I would drink tap water as it is tested and regulated by the EPA and it is more environmentally friendly," Ma said. "On the road, we may not have a choice."

If you do leave a water bottle sitting in your car and elect not to drink it, don’t just dump it on the ground—take Real Simple’s advice and use it to water your plants.

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