Originally Posted by passedpawn
Trivia: we can be thankful that water, unlike most other chemicals, expands when it freezes. Otherwise, lakes would freeze solid as the ice sank (it wouldnt' float!) and there would probably not be any life on this planet.
Water is fairly unique in this property. It does become more dense until it reaches about 40°F degrees, but below that it starts to expand. Once it crystalized into ice at 32°F it expands almost 10%! That's why ice floats, and it's also why your keg looks like it does now. Your keg is a small price to pay for life on earth.
+ this and it would be really difficult to make/chill beer without it. Side note if I remember correctly is also the only chemical (H20) that can be seen in all three forms in the same place, ice,water, and steam.