how water convert into ice

We know that the liquids expands on heating and contracts on cooling. But for water, when the temperature is between the range of 0 °C and 4 ºC, it shows anomalous behaviour. When the water is cooled from 4 °C  to 0 °C  it goes on expanding and when the water is heated from 0 °C  to 4°C  it goes on contracting. This behaviour of water between this temperature range is called anomalous behaviour of water. 

So, when the water is cooled from certain temperature to 4 °C it will contract initially but when temperature goes down from 4°C  to 0°C  it goes on expanding and when the temperature goes below 0°C  the water contracts and fuses to ice. In this way, water gets converted to ice.