Even as much as a few ounces is enough to kill.

The average healthy adult is made up of 55 to 60% water.

The average baby, on the other hand, is roughly 75% water.

And that difference is why babies shouldn't drink water before they're at least six months old.

Not from the tap or a well or a spring.

Plain water is just plain off limits.

You see, everyone's kidneys have a limit to how much water they can handle.

Break that limit, and the excess water will back up into your bloodstream, where it dilutes the salt, or sodium, in your blood.

Once your blood dips below 0.4 ounces of sodium per gallon, you're at risk of a condition called Hyponatremia.

It happens when your cells try to return sodium levels to normal by absorbing the extra water and swell up like a water balloon in the process,

causing complications like confusion, vomiting and muscle spasms.

Hyponatremia is common in marathon runners who drink too much too fast during a race without also providing enough sodium to balance out their blood.

And if you keep drinking, that excess water will eventually reach the cells in your brain.

By this point, you have a dangerous case of water intoxication, which affects roughly 200,000 Americans each year.

It occurs when your brain cells swell, which builds up pressure inside your skull that can lead to seizures, brain damage, and, in severe cases, death.

But don't worry, dying from water intoxication is extremely hard for a fully-grown human.

An adult would have to drink 2.5 to 5 gallons every few hours to reach that point.

But for newborns, it's a different story.

Their kidneys are about half the size of an adult's, so they can't hold much water to begin with.

And it takes just a few ounces to cause problems.

On top of that, their kidneys aren't developed enough yet to properly filter water, so any water that enters their body ends up in the circulatory system,

where it dilutes their blood and increases their water content by 7 to 8%.

But it's not just drinking straight H2O that poses a threat.

In fact, most cases of water intoxication in infants don't even involve a glass of water.

A common mistake is when people dilute baby formula too much by accident, or when parents dunk their infants up and down in a swimming pool,

and in the process the infant gulps in too much water.

It's important that if your baby is showing signs of water intoxication that you take them to the hospital immediately,

where a doctor will likely provide some form of fluids like intravenous saline solution to bring the infant's sodium levels up to normal.