You could say that at about 4 degrees celsius
clumps of water molecules start forming crystalline structure
s, which cause the water to increase its volume (expand
), but when it actually freeze
s it shrink
s as it creates larger, better fitting crystalline structures.
It's the expansion at 4C which makes your containers burst, not the freezing of the water (at 0C).
Incidently, if water is not allowed to expand to rearrange
itself, it stays in a semi-liquid state
. When the container bursts (depending on the conditions) the water may freeze midflight
. You might notice this as upward juts of ice in your icecubes
(when the outside of the ice freezes very quickly, before the inner water expands).