Water is an unusual chemical in that it occurs in nature in all three states: as a solid (ice), as a liquid (water), and as a gas (water vapour).

Pure water freezes at 0 degrees Celsius and boils at 100 degrees Celsius.

Water is also unusual in that it is lighter as a solid than it is as a liquid.

This is because water expands when it freezes—which is why it can break pipes in winter. Because ice is lighter than water, it floats.

If ice were heavier than water, ponds, lakes, oceans and seas would freeze from the bottom upwards, killing the fish and other living

 things.