“Heavy water” is just like normal water except -as you might guess- it’s a little heavier. It’s expensive to produce and difficult to come by, but I have this incredible urge to drink it. 1/

A regular water molecule [H₂O] is composed of one oxygen and two normal hydrogen atoms (one proton & electron). Heavy water [D₂O] is made of one oxygen and two deuterium atoms - an isotope of hydrogen with one proton, one neutron, and one electron. 2/

The inclusion of a neutron makes deuterium about twice as heavy as regular hydrogen. But since most water's mass comes from oxygen, this only makes heavy water around 11% heavier. But that’s enough to cause frozen heavy water to actually sink rather than float like normal ice. 3/

Heavy water molecules occur naturally but are rare and it’s really quite a pain to separate them out, so heavy water is typically only used for scientific research or in certain kinds of nuclear reactors. 4/

Ever since I learned about heavy water in undergrad I’ve wondered what exactly would happen if you drank it. So here it is. 5/

If you drink heavy water, the first thing it’ll do is make you dizzy. Your balance is partially mediated by fluid in your inner ear - if you change the weight of that fluid, your body won’t know how to account for it and it’ll throw off your balance. 6/

Say you keep drinking it anyway. In fact, say you drink *only* heavy water for days. Well, your biological processes will slow down. You see, the hydrogen bonds in deuterium are just stronger than in normal hydrogen. This severely inhibits cell division. 7/

Rats that are given *only* heavy water to drink die within a week of their body water reaching 50% heavy water. It is fatal, but only significant consumption. 8/

So really, humans can have little a heavy water, as a treat. 9.