Can You Drink Heavy Water? Is It Safe?

You can safely drink a small amount of heavy water, but drinking too much could make you sick or kill you.
You can safely drink a small amount of heavy water, but drinking too much could make you sick or kill you. (photo: Alchemist-hp)

You need water to live, but what happens if you drink heavy water? Is is safe? Radioactive? Here’s what you need to know.

What Is Heavy Water?

Heavy water is water in which the usual hydrogen atoms in H2O are replaced by deuterium atoms to form D2O. Regular hydrogen atoms (the protium isotope) contain one proton and no neutrons, while deuterium atoms contain one proton and one neutron. Like regular water, heavy water or deuterium oxide is colorless and participates in many of the same reactions as H2O. However, most people report the two types of water taste different. Heavy water has a slightly sweet flavor. Ice cubes made out of heavy water float in heavy water, but sink in regular water.

Deuterium and heavy water are not radioactive. However, the most common process used to isolate heavy water also concentrates tritiated water (T2O). Tritium atoms contain one proton and two neutrons, resulting in an unstable isotope. Basically, most heavy water is very slightly radioactive from the extra tritiated water. It’s no big deal, since regular drinking water contains minuscule amounts of both heavy water and tritiated water.

Watch what happens when you drink heavy water.

Is Drinking Heavy Water Safe?

While heavy water isn’t radioactive, it’s not entirely safe to drink. The issue is the extra mass of heavy water compared with ordinary water. Basically, the mass difference slows biochemical reactions that use water. Also, deuterium forms stronger hydrogen bonds than protium, resulting in a different reactivity.

You can drink a glass of heavy water and won’t suffer any ill effects. If you drink a few glasses, you might feel dizzy because some of the heavy water would change the density of fluid in your inner ear. If you only drink heavy water, eventually D2O molecules replaces enough H2O to cause problems.

How Drinking Heavy Water Could Kill You

Algae and bacteria can live with 100% heavy water and no regular water. Plant and animal cells are more complex, so too much heavy water results in sickness or death. One key issue is that heavy water disrupts mitosis, the type of cell division used to repair injuries and grow new cells. The mitotic spindles of cells containing too much heavy water simply aren’t able to equally divide a cell to form two identical new ones.

But, you have to continuously drink and eat only heavy water for several days to see an effect. Replacing 20% of regular water in cells with heavy water is survivable for humans and other mammals (although not recommended). Swapping 25% of water with heavy water causes (sometimes irreversible) sterilization. Replacing 50% of water with heavy water is lethal. It’s not a pretty death, either. Heavy water poisoning resembles radiation poisoning or cytotoxic poisoning from chemotherapy.


  • Dingwall, S.; et al. (2011). “Human Health and the Biological Effects of Tritium in Drinking Water: Prudent Policy Through Science – Addressing the ODWAC New Recommendation.” Dose-Response. 9 (1): 6-31. doi:10.2203/dose-response.10-048.Boreham
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