Distilled water is a highly purified form of water created by vaporizing it into steam and then condensing it back into a liquid. This process removes nearly all minerals, salts, and other dissolved impurities, making the water chemically closer to pure H₂O. This lack of contaminants influences its behavior when chilled and frozen.
The Basics of Freezing Distilled Water
Pure water freezes at a standard temperature of 0° Celsius (32° Fahrenheit) under normal atmospheric pressure. The difference between distilled water and tap water lies in the presence of dissolved solids. Tap water contains minerals and salts which slightly lower its freezing point, a principle known as freezing point depression. Pure distilled water consistently adheres to the 0°C freezing point and forms a more perfectly structured ice crystal lattice due to its lack of impurities.
Understanding Supercooling
Distilled water is particularly susceptible to a phenomenon called supercooling, where the water remains liquid even when its temperature drops below 0°C. For water to freeze, the molecules must arrange themselves into a hexagonal ice crystal structure, requiring a starting point called a nucleation site. In ordinary tap water, impurities like dust particles or minerals act as these sites, allowing ice crystals to form easily. Distilled water is so pure that it lacks these foreign particles, making it difficult for the molecules to spontaneously organize into a solid, allowing it to be cooled several degrees below its freezing point.
The supercooled liquid state is metastable, meaning it is unstable and can instantly freeze if disturbed. Introducing a disturbance, such as tapping the container or dropping a small piece of ice, provides the necessary energy or a seed crystal to initiate rapid crystallization. This sudden introduction of a nucleation site causes the supercooled water to visibly and quickly transform into solid ice.
Safe Storage and Container Selection
All water expands when it freezes, a unique property caused by the open, crystalline structure of ice. The volume increases by approximately 9% as it transitions from liquid to solid, generating immense pressure on the container. To safely freeze distilled water, select a container that can accommodate this volume change.
Avoid rigid materials like glass, which can crack or shatter under the pressure of the expanding ice, and opt instead for flexible plastic containers or ice cube trays. Leaving ample headspace is necessary; for a filled bottle, leave at least 10% of the volume empty. If the frozen water is intended for sensitive uses, ensure the storage container is clean and made of non-reactive materials to maintain purity.