Water freezes into ice at 32 degrees on which scale?

The freezing point describes the liquid to solid transition while the melting point is the temperature at which water goes from a solid (ice) to liquid water. In theory, the two temperatures would be the same, but liquids can be supercooled beyond their freezing points so that they don't solidify until well below freezing point. Ordinarily, the freezing point of water and melting point is 0 °C or 32 °F. The temperature may be lower if supercooling occurs or if there are impurities present in the water which could cause freezing point depression to occur. Under certain conditions, water may remain a liquid as cold as -40 to -42°F!

How can water remain a liquid so far below its usual freezing point? The answer is that water needs a seed crystal or other small particle (nucleus) on which to form crystals. While dust or impurities normally offer a nucleus, very pure water won't crystallize until the structure of liquid water molecules approaches that of solid ice.