Water in nature has three states: gas, solid and liquid. We call liquid water at normal temperature and pressure, gaseous water vapor and solid water ice.

The melting point of ice is 0℃ under normal pressure. When water freezes into ice at 0℃, its volume will increase by about111(the minimum water volume is 4℃). There is a relationship between the melting point of ice and pressure: below 2200 atmospheres, the melting point of ice decreases with the increase of pressure, but it is not obvious, about 130 atmospheres decreases 1 celsius; When the pressure exceeds 2200 atmospheres, the melting point of ice increases with the increase of pressure. The melting point of ice is-17℃ at 3530 atm, 0℃ at 6380 atm, 60℃ at 16500 atm, and the ice melts at 76℃ at 20670 atm, which is called "hot ice" in name. The density of ice is 0.92g/cm3 at 0℃, while the density of water is normally 1.00g/cm3, so ice can float on water.