Difference Between Water and Heavy Water

Isotopes refer to those members of the same family who share the same atomic number and vary slightly in atomic mass. The isotopes of the same element will form different compounds in combination with another element. The resulting compound slightly varies from the compound formed due to the combination of the isotope. These slight variations can also be noticed in water and heavy water.

Water vs Heavy Water

The main difference between water and heavy water is that while water has a chemical formula of H2O, heavy water has a chemical formula of D2O. Water contains one hydrogen atom in combination with one oxygen atom. However, heavy water contains one oxygen atom in combination with two deuterium atoms. Moreover, the refractive index and surface tension of water are higher in comparison to heavy water.

Water and Heavy Water

For all living organisms, water is the source of life. Hydrogen and oxygen join as a covalent bond in a fixed proportion to form water. The structure of the molecule is bent, forming an angle of 104.5°. Due to the high electronegative nature of oxygen atoms, oxygen atoms have a partial negative charge leading to the polarity of the O-H bond. Moreover, water molecules seem to aggregate on the surface in a short-range order.

As the name suggests, Heavy water contains heavier and higher hydrogen isotopes. At STP, heavy water has no color. It turns into a colorless and odorless liquid at room temperature. The mixture of normal and heavy water leads to the formation of a heterogeneous mixture. The electrolysis starts with a steel vessel as the cathode, a nickel sheet as the anode, and water and NaOH as the electrolyte. It was first discovered in 1932.

Comparison Table Between Water and Heavy Water

Parameters of ComparisonWaterHeavy Water
Chemical formulaH2O is the chemical formula of water.D2O is the chemical formula of heavy water, also referred to as deuterium oxide.
Molar massAccording to facts, it has a molar mass of 18g/mol.Heavy water has a molar mass of 20g/mol.
Boiling Point As facts say, it has a boiling point of 100 degrees Celsius.Heavy water has a boiling point of 101.4 degrees Celsius.
Freezing PointWater freezes at 0 degrees Celsius. But heavy water has a freezing point of 3.8 degrees Celsius.
DensityWater has a density of 997 kilogram / cubic meter.Heavy water has a density of 1.11 gram / cubic centimeter.

What is Water?

Water, covering a major part of our earth, is a chemical compound composed of hydrogen and oxygen joined in a covalent bond. The behavior of water is due to its properties, i.e., surface tension and viscosity. Water molecules also form hydrogen bonds. One can generally find water in three states. Ice is the solid-state formed by the freezing of water at 0°C. Water is the liquid form that covers about 71% of the earth. Water vapor is the gaseous state formed by boiling water at 100°C. 

Water is colorless, odorless, and tasteless in nature. Nearly all gases, sugars, salts, and acids easily mix and dissolve in water, due to which it’s known as a universal solvent. When combined with other solvents, it leads to the formation of azeotropes. The surface tension, specific heat, and thermal conductivity of water are higher when compared to other fluids and liquids. 

Moreover, water conducts very low amounts of electricity. However, the addition of ionic substances leads to the formation of ions in the liquid, which increases its conductivity. Water is essential for every moment of life. While 78% of our body is composed of water, an average healthy human needs the consumption of about 7 liters of water. Besides the human body, water also plays a significant role in agriculture, maintaining pH, washing, and maintaining water balance on earth. 

What is Heavy Water?

Deuterium oxide, also known as heavy water, is a chemical compound composed of deuterium and oxygen. Deuterium is a heavy isotope of H2, i.e., hydrogen, and thus has a higher atomic mass. Thus, the molar mass of heavy water is higher than that of normal water. Owing to the presence of deuterium, the properties of heavy water (i.e., both chemical and physical) differ slightly in comparison to normal water. Heavy water has a molecular mass of 20.02 grams/mole, a 1.107 g/mL density, and a dipole moment of 1.87 D. Moreover, the melting point of heavy water is 3.82°C, and its boiling point is 101.4°C. 

An alkali leads to the formation of heavy water in the presence of electrolysis of water. Moreover, heavy water is again categorized into semi-heavy, heavy-oxygen, and tritiated water. Semi-heavy water, also known as HDO, contains the chemical composition of one deuterium, one protium, and one atom of oxygen. In heavy-oxygen water, the presence of heavier isotopes of oxygen leads to its name. Tritiated water, also known as T2O, is super heavy water and radioactive due to the presence of tritium (the heaviest isotope of hydrogen).

Main Differences Between Water and Heavy Water

  1. The chemical consumption of water includes two atoms of hydrogen combined with one atom of oxygen. The chemical composition of heavy water includes two atoms of deuterium combined with one atom of oxygen. 
  2. Water has a broader structure owing to its hydrogen bonds. On the contrary, heavy water has a tetrahedral shape due to the higher number of hydrogen bonds present per heavy water molecule.
  3. Due to the low density, ice cubes made of water will not sink; instead, they will float on water. But, owing to the high density, ice cubes made out of heavy water will sink in water.
  4. Water has a pH of 7, which says that it’s neutral. But, heavy water has a pH of 7.44, which makes it a weaker acid. 
  5. Water is life for every living organism. Right from drinking to daily chores, water is essential for every activity of human life. Water is synonymous with survival. But, the use of heavy water is generally found in nuclear waters. Moreover, excessive consumption of heavy water can prove fatal. 


Although both water and heavy water slightly vary from each other in physical and chemical properties, they vary a lot in their consumption amounts. Regardless of the amount living organisms take, water is always helpful for the body. While low amounts of water intake can lead to diseases out of water deficiency, a high amount of water is never harmful to the body. However, heavy water shouldn’t be consumed in excess. Although it stands drinkable excessive consumption of heavy water will lead to a homeostatic imbalance in the body, thereby leading to death.


  1. https://pubs.acs.org/doi/pdf/10.1021/j100862a028
  2. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.101.065502
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