Is it safe to store plastic bottled water in a hot garage or car?
No. A 2026 zebrafish study found PET microplastics aged at high heat caused more gut and liver harm than fresh PET particles.
What's actually in it
Most single-use water bottles are made from PET plastic. Heat can age PET particles and make the plastic surface rougher and more reactive.
This is most relevant to bottled water stored in a hot garage, car, shed, or direct sun. A cool winter garage is not what the study tested.
What the research says
A 2026 study in Environmental Science & Technology compared fresh PET microplastics with PET microplastics aged at 60 C for 7 days. Zebrafish exposed for 80 days to the heat-aged PET particles had more gut retention, barrier damage, inflammation, microbiome disruption, and liver steatosis than fish exposed to fresh PET particles.
This is animal evidence. It does not prove one warm bottle causes liver disease. It does show that heat-aged bottle plastic deserves more caution than fresh PET.
What to do in the kitchen
Do not store plastic bottled water in a hot car or garage. Store emergency water in a cool, indoor place and rotate it.
For daily drinking at home, use glass or stainless steel when possible. If you buy bottled water, avoid bottles that sat in heat or sun.