Water is Weird!

As a gas, water is one of lightest known, as a liquid it is much denser than expected and as a solid it is much lighter than expected when compared with its liquid form.
At 4°C water expands on heating or cooling.
Hot water freezes faster than cold water and ice melts when compressed except at high pressures when liquid water freezes when compressed. No other material is commonly found as solid, liquid and gas.

clipped from www.lsbu.ac.uk Water phase anomalies e Water has unusually high melting point. [Explanation] Water has unusually high boiling point. [Explanation] Water has unusually high critical point. [Explanation] Solid water exists in a wider variety of stable (and metastable) crystal and amorphous structures than other materials. [Explanation] The thermal conductivity of ice reduces with increasing pressure. [Explanation] The structure of liquid water changes at high pressure. [Explanation] Supercooled water has two phases and a second critical point at about -91°C. [Explanation] Liquid water is easily supercooled but glassified with difficulty. [Explanation] Liquid water exists at very low temperatures and freezes on heating. [Explanation] Liquid water may be easily superheated. [Explanation] Hot water may freeze faster than cold water; the Mpemba effect. [Explanation] Warm water vibrates longer than cold water. [Explanation]