What Happens When You Drink Too Much Water?
Water is the safest thing you can swallow, so how can it kill you? The danger isn't how much you drink, it's how fast. Your kidneys can only drain about a litre an hour. Drink faster than that and the extra water thins the salt in your blood. Your cells swell, and the brain, boxed in by the skull, has nowhere to grow. At the 2002 Boston Marathon, one runner in eight finished with blood that thin.
The rule: drink when you're thirsty, and let the drain keep up.
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Transcript
Water is about the safest thing you can swallow. Yet drunk fast enough, it can kill you. Because the danger isn't how much you drink, it's how fast. Your kidneys can only drain about a litre an hour. Pour faster than that, and the extra water stays in your blood, thinning out its salt. Now your cells are saltier than the blood around them, so water rushes in, and every cell swells.
Elsewhere, that's just puffiness. But your brain sits inside a hard skull, with nowhere to grow: headache, confusion, seizures. At the 2002 Boston Marathon, one runner in eight finished with blood that thin. So drink when you're thirsty, and let the drain keep up.
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