“Leaving plastic water bottles in a hot car makes the water dangerous.”
A plastic water bottle left in a hot car for an afternoon does not become dangerous to drink.
You do not need to throw out a bottle of water because it sat in a warm car for a while. The release that matters takes many days to weeks of extreme heat, so the simple habit is to not store water in a hot car or garage for long periods.
Keep bottled water out of direct sun and hot cars for long stretches, and use up or replace bottles that have been stored in high heat for weeks.
Lab tests show heat does make plastic bottles release more antimony, but it takes days to weeks of very high heat to pass the U.S. drinking-water limit, so the danger claim is much bigger than the real effect. Confidence is limited because the evidence comes from a few lab studies of bottles, not studies of people.
A plastic water bottle left in a hot car for an afternoon does not become dangerous to drink. Heat does make bottles release more antimony, a metal used to make the plastic, but based on lab tests, researchers estimated it would take about 12 days at 158 F (70 C), or about 5 weeks at 149 F (65 C), for the water to pass the U.S. drinking-water limit.
Most water bottles are made of a plastic called PET. In a U.S. lab study of nine bottled waters, antimony started far below the U.S. limit of 6 parts per billion and did not change after three months at room temperature, about 72 F (22 C). Heat sped up its release. From those tests, the researchers estimated the time needed to pass the limit at about 176 days at 140 F (60 C), 38 days at 149 F (65 C), 12 days at 158 F (70 C) and 2.3 days at 176 F (80 C). The authors noted that summer temperatures inside cars and garages in Arizona can go above 149 F (65 C). A second study of 16 bottle brands in China found that after one week at 158 F (70 C), antimony was still under the U.S. limit in all of them, and BPA levels were very low. In the worst case that study tested, four weeks at 158 F (70 C), the estimated daily antimony intake from one brand went over the U.S. EPA's long-term daily safety level, slightly for adults and about three and a half times for children.
- Westerhoff P, Prapaipong P, Shock E, Hillaireau A. Antimony leaching from polyethylene terephthalate (PET) plastic used for bottled drinking water. Water Research. 2008;42(3):551-556. DOI: 10.1016/j.watres.2007.07.048. PMID: 17707454
- Fan YY, Zheng JL, Ren JH, Luo J, Cui XY, Ma LQ. Effects of storage temperature and duration on release of antimony and bisphenol A from polyethylene terephthalate drinking water bottles of China. Environmental Pollution. 2014;192:113-120. DOI: 10.1016/j.envpol.2014.05.012. PMID: 24907857