Heavy Water

Heavy Water


Water is a transparent and nearly colorless chemical substance that is the main constituent of Earth’s ocean, streams, and lakes. We may have heard of heavy water and wondered how it was different from ordinary water. Heavy water is water that contains heavy hydrogen or deuterium. The different properties and uses of heavy water are discussed below.

What is Heavy Water?

Heavy water or deuterium oxide (D2O) is a form of water that contains a large amount of the hydrogen isotope deuterium which is also known as heavy hydrogen. Deuterium differs from the hydrogen which is usually found in water. Heavy water may be deuterium protium oxide (DHO) or deuterium oxide (D2O).

The increase in mass due to the presence of deuterium gives it a different chemical and physical property compared to normal water.

Some other heavy forms of water are:

  • Tritiated water
  • Heavy-oxygen water
  • Semiheavy water

Properties of Heavy Water

Heavy water contains a huge amount of deuterium oxide. The properties of heavy water are mentioned in the table below.


H2O (Light water)

D2O (Heavy water)

Boiling point 100.0 °C (212 °F) (373.15 K) 101.4 °C (214.5 °F) (374.55 K)
Freezing point 0.0 °C (32 °F) (273.15 K) 3.82 °C (38.88 °F) (276.97 K)
Temp. of maximum density 3.98 °C 11.6 °C
Density at STP (g/mL) 0.9982 1.1056
Surface tension (at 25 °C, N/m) 0.07198 0.07187
Dynamic viscosity (at 20 °C, mPa·s) 1.0016 1.2467
Heat of vaporisation (kJ/mol) 40.657 41.521
Heat of fusion (kJ/mol) 6.00678 6.132
pKb (at 25 °C) 7.0 7.44 (“pKb D2O”)
pH (at 25 °C) 7.0 7.44 (“pD”)
Refractive index (at 20 °C, 0.5893 μm) 1.33335 1.32844

Uses of Heavy Water

India is one of the world’s largest producers of heavy water through its Heavy Water Board and also exports to countries like The United States and The Republic of Korea. Heavy water is used in certain types of nuclear reactors, where it acts as a neutron moderator to slow down neutrons. The different applications and uses of heavy water are mentioned below.

  • Nuclear magnetic resonance
  • In Organic chemistry
  • Fourier transform spectroscopy
  • Neutron moderator
  • Neutrino detector
  • Metabolic rate testing in physiology and biology
  • Tritium production

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Practise This Question

D2O is used more in