Apart from tasting yucky, the main health concerns here are microplastics and chemicals leaching from the bottle.
There are several studies that have shown that antimony (which causes symptoms like arsenic poisoning at high doses) leaches into the water from PET plastic typically used in disposable water bottles.
This leaching increases sharply above 45⁰C (113⁰F), but even then, virtually every study has found that antimony levels remain comfortably below the WHO drinking water limits.
Microplastics are already present in bottled water to some extent, but a 2024 study at Zhejiang University in China found that temperature doesn’t affect their concentration measurably until you get over 80⁰C (176⁰F).
This article is an answer to the question (asked by Kian Pearce, Chichester) 'Is it safe to drink from a plastic bottle that's been left in a hot car?'
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