Water left in a car exposed to high temperatures and direct sunlight can become unsafe to drink due to chemical migration from the plastic container and bacterial growth. ^[1] Ashley C. Miller, M.P.H., CP-FS, senior program coordinator at the National Environmental Health Association, stated that refilling clean and undamaged single-use plastic bottles one or several times with safe drinking water is unlikely to cause significant food safety risks. ^[2] A study cited by the Italian newspaper Il Post estimated that water left at 60°C for approximately 176 days, 70°C for 12 days, or 80°C for two days would exceed US safety limits for antimony levels. ^[3] Cooling, freezing, or boiling water that has been exposed to heat in a car does not remove migrated substances or reverse the chemical changes. ^[4] Most water bottles are made of PET (polyethylene terephthalate), which releases substances into the water more rapidly when exposed to high temperatures and direct sunlight. ^[5] Approximately 1.3 billion single-use plastic water bottles are used globally every day due to convenience and lack of access to clean water. ^[6] Ashley C. Miller noted that risks increase if the bottle is damaged, as scratches or dents near the cap make it difficult to clean and allow microorganisms to form biofilms. ^[7] Brian Labus, Ph.D., an epidemiologist from the University of Nevada, warned that filling bottles with liquids other than plain water, such as milk, juice, or soda, creates a high opportunity for bacteria to multiply rapidly. ^[8]