UF soil and water science professor Lena Ma led a research team that studied chemicals released in 16 brands of bottled water kept at 158 degrees Fahrenheit for four weeks, what researchers deemed a “worst-case scenario” for human consumption.
The UF scientist warned against leaving bottled water in a hot garage for weeks on end or in your car all day during the summer.

Antimony concentration was the main concern in our study. The concentrations increased in each of the sample during storage period at all temperatures. The results for different conditions were as follow: at 40°C, in outdoor and at room temperature the Sb concentrations were below the MCLs, i e. 6 ppb. However, at 65°C and 80°C for longer storage times Sb concentration exceeded the MCLs, and variations between the samples were significant (p?=?0.05). Storage time and temperature effects on the content of some other trace elements such as Al, Fe were also significant (p?=?0.05).
Conclusion
By increasing the duration of storage time and temperatures, antimony leaching from the PET bottles into the bottled water increased. The concentration of Al demonstrated an increase in higher temperatures and storage duration, whereas the content of Fe demonstrated no significant differences.
Last of all, the consumer should not leave the bottled waters inside their vehicles’ and/or closed areas due to the high temperatures which occur in these conditions.
The five storage conditions designed for the investigation of the samples were, storage at room temperature (25?±?2.6°C), outdoors and sunlight (31?±?4.6°C) and 40°C and the experiment intervals were defined as follows, weeks 0 (immediately after receiving), 1, 2, 4, 6 and 8 were performed. Storage at 65°C, and the experiments was done in days zero (immediately after receiving), 3, 7 and weeks 2, 4 and 6. Storage at 80°C at test days zero (immediately after receiving), 1, 2, 3, 4 and 7 was considered for the other storage condition.