Water bottles do not freeze in the freezer section of grocery stores and supermarkets due to a phenomenon called supercooling. Supercooling occurs when a liquid is cooled below its freezing point without actually solidifying. This can happen when the water is very pure and lacks impurities or nucleation sites, which are points where ice crystals can start forming.
In a typical freezer, the temperature is set below the freezing point of water, usually around -18 degrees Celsius (0 degrees Fahrenheit). When a water bottle is placed in the freezer, it cools down but remains in a liquid state because there are no impurities or nucleation sites to initiate the formation of ice crystals. Without these starting points, the water molecules remain in a supercooled state even though they are below the freezing point.
However, supercooling is not a stable state, and it can be easily disrupted. Any disturbance or introduction of an impurity, such as tapping the bottle or opening it, can trigger the rapid crystallization of the supercooled water, causing it to freeze almost instantly.
It's worth noting that not all water bottles exhibit supercooling. Some plastic bottles, particularly those made from softer plastic or containing additives, can deform or rupture under the extreme cold temperatures of a freezer. So, it's always advisable to check the specific instructions or recommendations provided on the water bottle's packaging.