If you don't pressurize a bottle of water before putting it in the freezer, there is a risk of the bottle rupturing or exploding due to the expansion of water as it freezes.
When water freezes, it undergoes a unique property known as "expansion upon freezing." Unlike most substances that contract as they solidify, water expands as it freezes into ice. This expansion can exert significant pressure on the walls of a container, including a bottle.
If the bottle is tightly sealed and there's no room for the expanding ice to accommodate the increased volume, the pressure inside the bottle will build up until it reaches a point where the bottle cannot contain it anymore. This can lead to the bottle bursting open, causing a mess and potentially posing a safety hazard.
To avoid this, it's essential to leave some room for expansion when freezing liquids, including water. If using a plastic bottle, you should leave some empty space at the top to allow for the ice to expand without causing damage. Alternatively, you can use containers specifically designed for freezing liquids, which have space built into the design to accommodate expansion.
However, it's crucial to note that glass containers are particularly susceptible to breaking under these circumstances, so it's generally not recommended to freeze water in glass bottles without leaving adequate room for expansion.
In summary, if you want to freeze water or any other liquid in a container, ensure that you provide enough space for the liquid to expand during the freezing process to prevent the container from rupturing or exploding.