Contributors: Lucas Simonds
Distilled water is a form of water which has been purified through a process of distillation. In this process the water is heated to the point of vaporization and then condensed on a cool surface where it is then collected as liquid water. The distillation process is capable of producing water that is up to 99.9% pure; most of the impurities found in water, such as salts, have a significantly higher boiling point than water, and are therefore separated from the water as it vaporizes. In addition, further distillations are effective in producing water of a higher level of purity for applications which may require it (Conti 2005: 441).
Synonyms in English
In the context of conservation, distilled water is useful in a number of applications. Because of the high level of purity achieved through distillation, distilled water is often recommended for use in storage solutions, the purpose being to avoid the introduction of new contaminants to already fragile objects (Hamilton 1997: 67). Caution must be taken, however, as distilled water exposed to air will quickly absorb carbon dioxide and produce carbonic acid. Over a period of 24 hours this reaction can result in a pH between 5.5 and 6 (Conti 2005:442), which can trigger adverse reactions with some materials. For use with metals in particular, it is advisable to monitor the pH of distilled water, as it has the potential to be highly corrosive (Hamilton 1997:67), the natural acidification of distilled water can also be counteracted through boiling, which will generally return the pH to 7 within 5-10 minutes (Conti 2005:442).
In addition to its use in the storage of objects, distilled water is commonly used in desalination baths. During the early stages of desalination the concentration of chlorides in an object is generally high enough to allow for their diffusion into tap water. As this concentration decreases, however, water of a higher level of purity is required for diffusion to continue. Therefore, in the final stages of most desalination treatments it is often necessary to use distilled water because of its very high level of purity (Cronyn 1990:1910).
Cronyn, J.M. 1990. Elements of Archaeological Conservation. New York, New York: Routledge
Conti, Aldo, Distilled Water in Lehr, Jay, Jack Keeley, and Janet Lehr, eds. 2005. Water Encyclopedia, vol. 4. Oceanography; Meterology; Physics and Chemistry; Water Law; and Water History, Art, and Culture. Hoboken, New Jersey: John Wiley & Sons.