How long it takes water to become ice depends on the temperature of the water, how much water you have and how cold the freezing environment is. For water to freeze, it must reach 32 degrees Fahrenheit.
At 40 degrees Fahrenheit, water is a bit denser than it is at its freezing temperature of 32 degrees Fahrenheit. When at the freezing temperature, it is approximately 8 percent less dense than water in its liquid state. Once ice is completely frozen, rapid cooling can result in a change in density, because even when ice is solid the molecules continue to shift.