Distilled water is purified by heating it to steam and then condensing it back into a liquid, a process that removes dissolved minerals, ions, and other particulates. The simple answer to whether this highly purified water freezes is yes, but the conditions are often different from tap water. While ordinary water typically begins to freeze at its standard temperature of 0°C (32°F), distilled water frequently needs to be cooled much lower. This difference stems from the unique physics governing the formation of ice crystals in a highly pure liquid.
The Fundamental Physics of Freezing
Freezing, which is the phase change from a liquid to a solid, requires water molecules to slow down and arrange themselves into the repeating, hexagonal lattice structure of ice. This molecular organization is an energetic process that does not spontaneously happen the moment the temperature drops below the freezing point. For the liquid-to-solid transformation to begin, a starting point is necessary, which is a concept known as nucleation.
Nucleation involves the initial formation of a stable, microscopic ice seed, or nucleus, around which water molecules can attach and build the crystal structure. In typical water, this process is heterogeneous, meaning the ice forms around a pre-existing surface or impurity. These nucleation sites are commonly dust particles, dissolved minerals, air bubbles, or imperfections on the container walls. The presence of these sites lowers the energy barrier for crystallization, allowing water to freeze right at or very near 0°C.
Why Distilled Water Behaves Differently
The distillation process strips water of its dissolved solids, ions, and suspended particles, resulting in nearly pure H₂O. This high purity significantly reduces the number of available heterogeneous nucleation sites. Unlike tap water, distilled water lacks the microscopic “scaffolding” that helps organize the first ice crystals.
Because these starting points are absent, distilled water must rely on homogeneous nucleation, which is the spontaneous clustering of water molecules into a stable ice structure without an external trigger. This spontaneous formation requires a much lower temperature to overcome the energy barrier. For water to undergo true homogeneous nucleation, it must be cooled to an extremely frigid temperature, often around -39°C (-38°F) or even as low as -48.3°C (-55°F). Due to the lack of impurities, distilled water is far more likely to remain liquid even when colder than 0°C.
Understanding Supercooling
The phenomenon where a liquid is cooled below its standard freezing point without solidifying is called supercooling. Because distilled water lacks the necessary impurities to act as nucleation sites, it is particularly susceptible to this state. Although the water molecules have slowed down significantly at these sub-zero temperatures, they are still unable to spontaneously lock into the crystalline ice structure.
A liquid in a supercooled state is considered metastable, meaning it is delicately balanced and will freeze instantly if disturbed. Introducing a physical trigger, such as shaking the container or dropping in a small piece of ice, provides the surface required for the molecules to align. This disturbance acts as the nucleation site, causing the liquid to flash-freeze into ice almost instantaneously. This snap-freezing effect is the most recognizable consequence of the purity of distilled water.