Humans have a hard time keeping water bottles in cars in the sun over a long period of time without putting it in a cooler or in some other means to keep the bottles from getting too hot.
The key with sunlight is light’s ability to penetrate through plastic and create enough heat at its core so that this heat then radiates back out into the bottle, causing an increase in temperature that eventually ruins your bottled water. In addition, even though there still may be liquid inside of your cooler, these liquids will also come into contact with both direct sunlight and sun’s radiation, making them difficult to maintain during the summer months when temperatures can reach up towards 100 degrees Fahrenheit.