Water typically becomes ice when its temperature reaches freezing levels. When water temperature falls to approximately 0 degrees Celsius, it freezes and solidifies as ice in most cases. There are certain cases in which water gets below 0 degrees Celsius and still remains in its liquid form.
Water molecules have more energy in liquid form than in solid form. As the temperature of the liquid becomes lower, the energy is reduced, which causes the water molecules to slow down. When the temperature reaches freezing level, the molecules stick together to form solid ice. However, the molecules are still in motion.
There is more to water freezing than just getting cold. There needs to be a crystal seed for the water to become ice. The seed can be any impurity in the water for ice crystals to grow. The container holding the water is also a factor in the freezing of water. Other factors that influence water freezing include density, pressure, movement and other dissolved solids.
Not all water will turn into ice at 0 degrees Celsius. In some cases, water can cool down to 40 below. This process is known as super cooling. This only happens when water is completely pure and in a very smooth container.