When placing bottles of water in the freezer, it's generally recommended not to fill them up to the top because water expands as it freezes. As water freezes, it undergoes a physical expansion, and this expansion can cause the bottle to crack or burst under the pressure.
When water freezes, it increases in volume by about 9%. If a bottle is filled to its maximum capacity, there won't be enough space for the water to expand, leading to the potential for the bottle to rupture.
To prevent this from happening, it's advisable to leave some empty space at the top of the bottle before freezing it. This extra space accommodates the expansion of water as it turns into ice, reducing the risk of the bottle breaking and making a mess in your freezer.
Leaving around 10-20% of the bottle empty should provide enough room for the ice to expand without causing any damage.