Can You Drink Heavy Water?

Is it radioactive or safe to drink?

Erlenmeyer Flask with Laboratory Glassware in the Background
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You need ordinary water to live, but have you ever wondered whether or not you can drink heavy water? Is it radioactive? Is it safe?

Chemical Composition and Properties of Heavy Water

Heavy water has the same chemical formula as any other water—H2O—with the exception that one or both of the hydrogen atoms are the deuterium isotope of hydrogen rather than the regular protium isotope (which is why heavy water is also known as deuterated water or D2O).

While the nucleus of a protium atom consists of a solitary proton, the nucleus of deuterium atom contains both a proton and a neutron. This makes deuterium about twice as heavy as protium, however, since it's not radioactive, heavy water is not radioactive either. So, if you drank heavy water, you wouldn't need to worry about radiation poisoning.

Are Small Quantities of Heavy Water Safe?

Just because heavy water isn't radioactive doesn't mean it's completely safe to drink. If you ingested enough heavy water, the biochemical reactions in your cells would be affected by the difference in the mass of the hydrogen atoms and how well they form hydrogen bonds.

You could consume a single glass of heavy water without suffering any major ill effects, however, should you drink any appreciable volume of it, you might begin to feel dizzy. That's because the density difference between regular water and heavy water would alter the density of the fluid in your inner ear.

How Heavy Water Affects Mitosis in Mammals

While it's unlikely you could drink enough heavy water to really harm yourself, the hydrogen bonds formed by deuterium are stronger than those formed by protium. One critical system affected by this change is mitosis, the cellular division used by the body to repair and multiply cells. Too much heavy water in cells disrupts the ability of mitotic spindles to equally separate dividing cells.

Theoretically, you'd have to replace 20 to 50% of the regular hydrogen in your body with deuterium to experience symptoms ranging from distressing to catastrophic. For mammals, replacing 20% of the body's water with heavy water is survivable (although not recommended); 25% causes sterilization, and about 50% replacement is lethal.

Other species tolerate heavy water better. For example, algae and bacteria can live on 100% heavy water (no regular water).

The Bottom Line

Since only about one water molecule in 20 million naturally contains deuterium—which adds up to about five grams of natural heavy water in your body and is harmless—you don't really need to worry about heavy water poisoning. Even if you did drink some heavy water, you'd still be getting regular water from food.

In addition, the deuterium wouldn't instantly replace every molecule of ordinary water in your body. You'd need to drink heavy water for several days to see a negative result, so as long as you don't do it longterm, it's okay to drink.

Fast Facts: Heavy Water Bonus Facts

Bonus Fact 1: If you did drink too much heavy water, even though heavy water is not radioactive, your symptoms would mimic radiation poisoning. This is because both radiation and heavy water damage the ability of cells to repair their DNA and replicate.

Bonus Fact 2: Tritiated water (water containing the tritium isotope of hydrogen) is also a form of heavy water. This type of heavy water is radioactive. It's also much rarer and more expensive. It's created naturally (although very infrequently) by cosmic rays and can also be produced in nuclear reactors by humans.