We couldn't live without water. But if we drink too much, it can wreak havoc on our brain and body. Drinking more water than your kidneys can process can throw your blood sodium levels out of balance. That's called water intoxication. And in extreme cases, it can cause brain damage, comas, and even death.

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Following is a transcript of the video:

What do you think of when you hear the word poison? Arsenic? Cyanide? How about water?

Life couldn’t exist without water. But in the right circumstance... Water can be as dangerous as any poison.
Here's what happens when you drink too much water.
Your kidneys filter out excess waste and water from your bloodstream. But they can only process 800-1,000 mL of water an hour. And if you somehow manage to drink more than that without throwing up, you can run into trouble. Because you’re drinking faster than your kidneys can process it. So the excess ends up in your cells.

Normally, your cells are surrounded by a carefully-balanced solution of sodium and water, which flows in and out through tiny holes in the cellular membrane, so it keeps the sodium concentration both in and out of the cell balanced.

But when you drink too much water, the sodium solution gets diluted. It’s not salty enough. So some of that extra water rushes into the cell to restore balance and that causes it to swell up.

Doctors call this water intoxication and it’s a big problem. Now, most of your cells can handle the swelling to a degree since soft, flexible tissue like fat and muscle can stretch.

But for the cells in your brain, it’s another story, because your skull isn’t stretchy.
It’s bone. It’s hard — like a rock.

So, as your brain swells, it builds up the pressure in your head.

At first, you might experience headaches, confusion, or drowsiness.

But as the pressure increases, you risk brain damage, coma, and even death. And it could all be over in less than ten hours.

A 64-year-old woman, for example, died the same evening after drinking between 30-40 glasses of water. And a group of US Army trainees suffered vomiting and seizes after downing over 2 liters per hour after a tough day of training.

But it’s marathon runners who need to be especially careful. A study found that 1 in 6 marathon runners develop at least mild water intoxication because the race stresses their body, including the kidneys. So, they don’t excrete water as efficiently, which can cause water to back up into the blood more easily.

People with certain kidney issues are also vulnerable since they can’t properly process water and the problem isn’t unique to water.

For example, the same thing can happen if you down too much beer at once. That’s called potomania.

The good news is that there’s an easy way to stay safe. The average healthy adult needs somewhere around 3-4 liters of water a day. And since this can come from food and other drinks too, drink when you’re thirsty, and then stop.