Heavy Water | Definition, Formula, Preparation, & Facts - Britannica

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External Websites

• National Center for Biotechnology Information - PubMed Central - Research Progress in the Medical Application of Heavy Water, Especially in the Field of D2O-Raman Spectroscopy
• Cell Press - Effect of Heavy Water on Protein Flexibility (PDF)
• PNAS - Tracking heavy water (D2O) incorporation for identifying and sorting active microbial cells
• Energy Education - Heavy water
• Chemistry LibreTexts - Deuterated Compounds
• Nature - Communications Biology - Sweet taste of heavy water
• CORE - Measurement of the total cross section of heavy water in the 0.1 meV1 eV energy range at 20 and 50 ◦C (PDF)
• Chemistry World - Heavy water
• The Royal Society of Chemistry - RSC Advances - Heavy water recycling for producing deuterium compounds
• U.S. Department of Energy Office of Scientific and Technical Information - Heavy Water

heavy water chemical compound Ask Anything Homework Help Also known as: D2O, deuterium oxide Written and fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Jan. 22, 2026 •History Britannica AI Ask Anything Table of Contents Table of Contents Ask Anything

heavy water (D2O), water composed of two atoms of deuterium, the hydrogen isotope with a mass double that of ordinary hydrogen, and one atom of oxygen. (Ordinary water has a composition represented by H2O.) Thus, heavy water has a molecular weight of about 20 (the sum of twice the atomic weight of deuterium, which is 2, plus the atomic weight of oxygen, which is 16), whereas ordinary water has a molecular weight of about 18 (twice the atomic weight of ordinary hydrogen, which is 1, plus oxygen, which is 16).

Also called: deuterium oxide (Show more) Key People: Gilbert N. Lewis Harold C. Urey Bruno Pontecorvo (Show more) Related Topics: water (Show more) On the Web: Chemistry LibreTexts - Deuterated Compounds (Jan. 22, 2026) (Show more) See all related content

As obtained from most natural sources, ordinary water contains about one deuterium atom for every 6,760 ordinary hydrogen atoms. Continued electrolysis of hundreds of liters of water until only a few milliliters remain yields practically pure deuterium oxide. This operation, until 1943 the only large-scale method used, has been superseded by less expensive processes, such as the Girdler sulfide process (deuterium is exchanged between hydrogen sulfide [H2S] and water) and fractional distillation (D2O becomes concentrated in the liquid residue because it is less volatile than H2O). The heavy water produced is used as a moderator of neutrons in nuclear power plants. In the laboratory heavy water is employed as an isotopic tracer in studies of chemical and biochemical processes.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Erik Gregersen.