What Is Heavy Water?

Heavy water
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You may have heard of heavy water and wondered how it was different from ordinary water. Here's a look at what heavy water is and some heavy water facts.

Heavy Water Definition

Heavy water is water that contains heavy hydrogen or deuterium. Deuterium differs from the hydrogen usually found in water, protium, in that each atom of deuterium contains a proton and a neutron. Heavy water may be deuterium oxide, D2O or it may be deuterium protium oxide, DHO.

Heavy Water Abundance

Heavy water occurs naturally, although it is much less common than regular water. Approximately one water molecule per twenty million water molecules is heavy water.

So, heavy water is an isotope that has more neutrons than ordinary water. Do you expect this makes it radioactive or not? Heavy water is not radioactive. Here's how it works.


If enough heavy water is ingested to replace 25% to 50% of water in the human body, heavy water poisoning may occur. However, because of the high turnover rate of water, drinking a small amount of the substance causes no ill effects. In fact, American physicist Harold Urey once drank heavy water to learn whether it tasted different from ordinary water (in the name of science, of course).


  • International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN 0-85404-438-8. p. 306.
  • Mosin, O. V, Ignatov, I. (2011) Separation of Heavy Isotopes Deuterium (D) and Tritium (T) and Oxygen (18O) in Water Treatment, Clean Water: Problems and Decisions, Moscow, No. 3–4, pp. 69–78.
  • Urey, HC; Failla, G (March 15, 1935). "Concerning the Taste of Heavy Water". Science. 81 (2098): 273. doi:10.1126/science.81.2098.273-a
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Helmenstine, Anne Marie, Ph.D. "What Is Heavy Water?" ThoughtCo, Feb. 16, 2021, thoughtco.com/what-is-heavy-water-609412. Helmenstine, Anne Marie, Ph.D. (2021, February 16). What Is Heavy Water? Retrieved from https://www.thoughtco.com/what-is-heavy-water-609412 Helmenstine, Anne Marie, Ph.D. "What Is Heavy Water?" ThoughtCo. https://www.thoughtco.com/what-is-heavy-water-609412 (accessed February 8, 2023).