The Ocean Within Us

BBC · Sep 28, 2026 · 28m

Here's a little fact you might have heard before: Humans are around 70% water. About the same percentage as a sweet potato, incidentally. But what does that actually mean? Sure, there's blood, that accounts for some of it. And the lymphatic system has a fair amount too, sloshing around. There's water in each of our cells. But that doesn't add up to the full 70% - where is the rest of it? In 2018, a scientific paper was published which gives a tantalising clue. The authors revealed for the first time that our 'interstitial spaces' - those gaps, between our bones and joints and all of our…