Fresh water freezes at 32 degrees Fahrenheit, which is 0 degrees Celsius and 273.15 degrees on the Kelvin scale. Seawater freezes at a slightly lower temperature than fresh water due to its high salt content.
Although water has standard freezing temperatures, scientists have found water in its liquid form at temperatures below -40 degrees Fahrenheit. As water grows colder, its molecular structure changes shape, which alters the density of the water and increases its heat capacity. At -55 degrees Fahrenheit, the molecules become tetrahedrons, and that difference in structure changes the way the molecules react to heat and cold.
All things freeze at 0 degrees Kelvin, also known as Absolute Zero. That temperature represents a total absence of heat, and molecular motion stops.