Water has many unique properties which are very important for the existence of life as we know it on the Earth. Although we are surrounded by water, most is not drinkable. Water is the only common, safe substance that can exist in all three states at the same time on the surface of the Earth. In the liquid state, water has no definite shape. Instead, it takes the shape of any container it is poured to with the upper surface of the water always horizontal.
Liquid water expands rather than contracts when it freezes.
Water, like other materials will contract as it is cooled. At 4 C however, water starts to expand as it begins to solidify. As a result, ice is less dense than liquid water. This means that ice floats on top of liquid water and bodies of water freeze from the top down. Lakes and streams usually do not freeze solid in cold climates as the layer of ice on the top acts as an insulator.