Water generally becomes more dense when it is cooled however unlike most things liquid water expands when it freezes into a solid. This is because the water molecules, when they are in the form of ice, arrange themselves in a spacious rigid framework in which they are relatively far apart from one another.They begin to loosely arrange themselves into the rigid ice framework. This process involves forming bonds with one another. While they do not totally freeze in place until they reach 0 ?C they do, on average, end up getting farther apart from one another as they approach 0 ?C. It is at the temperature of 4 ?C that their tendency to get closer because they are slowing down equals their tendency to get further apart because they are bonding. The density of water will be a maximum at the temperature at they are the closest. Because below that temperature the water molecules start to form networks of hydrogen bonds, which causes them to all move slightly apart. The spacing between molecules in the hydrogen-bonded network is larger than the spacing between molecules not in the network.