Water expands when freezing
Have you ever wondered why ice cubes float in your lemonade? If you think that’s because water is special, then you are right. Despite most substances shrinking as they get colder, water has a pretty strange behavior, as it reaches its maximum density at 4 degrees Celsius. As it goes below that temperature and it starts to freeze, water expands its volume by up to 9%. This happens because water molecules are connected through something called hydrogen bonds, which is something that most substances don’t have. When water goes below the 4 degrees threshold, these bonds arrange the molecules in beautiful hexagonal structures, increasing the space between them. The fact the ice floats on water is really good news, since otherwise we would have no Antarctica, polar bears or Titanic movie.
Here is a nice explanation of how that happens