Heavy Water Facts

Learn more about heavy water properties and characteristics

Sample of Heavy Water
 By Alchemist-hp (talk) (www.pse-mendelejew.de) (Own work) [FAL], via Wikimedia Commons

Heavy water is deuterium monoxide or water in which one or more of the hydrogen atoms is a deuterium atom. Deuterium monoxide has the symbol D2O or 2H2O. It is sometimes referred to simply as deuterium oxide. Here are facts about heavy water, including its chemical and physical properties.

Heavy Water Facts and Properties

CAS number7789-20-0
molecular formula2H2O
molar mass20.0276 g/mol
exact mass20.023118178 g/mol
appearancepale blue transparent liquid
density1.107 gm/cm3
melting point3.8°C
boiling point101.4°C
molecular weight20.0276 g/mol
vapor pressure16.4 mm Hg
refractive index1.328
viscosity at 25°C0.001095 Pa s
specific heat of fusion0.3096 kj/g

Heavy Water Uses

  • Heavy water is used as a neutron moderator in some nuclear reactors.
  • Deuterium oxide is used in nuclear magnetic resonance (NMR) spectroscopy in aqueous solutions involving the study of a hydrogen nuclide.
  • Deuterium oxide is used in organic chemistry to label hydrogen or to follow reactions involving water.
  • Heavy water is often used instead of regular water in Fourier Transform Infrared Spectroscopy (FTIR) of proteins.
  • Heavy water-moderated reactors are used to produce another isotope of hydrogen — tritium.
  • Heavy water, made using deuterium and oxygen-18, is to test human and animal metabolic rates via the doubly labeled water test.
  • Heavy water has been used in a neutrino detector.

Radioactive Heavy Water?

Many people assume heavy water is radioactive because it uses a heavier isotope of hydrogen, is used to moderate nuclear reactions, and is used in reactors to form tritium (which is radioactive).

Pure heavy water is not radioactive. Commercial grade heavy water, much like ordinary tap water and any other natural water, is slightly radioactive because it contains trace amounts of tritiated water. This does not present any sort of radiation risk.

Heavy water used as a nuclear power plant coolant contains significantly more tritium because neutron bombardment of the deuterium in heavy water sometimes forms tritium.

Is Heavy Water Dangerous To Drink?

Although heavy water isn't radioactive, it's still not a great idea to drink a large volume of it because the deuterium from the water doesn't act quite the same way as protium (a normal hydrogen isotope) in biochemical reactions. You would not suffer harm from taking a sip of heavy water or drinking a glass of it, but if you only drank heavy water, you'd replace enough protium with deuterium to suffer negative health effects. It's estimated you would need to replace 25-50% of the regular water in your body with heavy water to be harmed. In mammals, 25% replacement causes sterility. 50% replacement would kill you. Keep in mind, much of the water in your body comes from the food you eat, not just water you drink. Also, your body naturally contains small amounts of heavy water and every smaller amount of tritiated water.

Primary Reference: Wolfram Alpha knowledgebase, 2011.