We need to be hydrating! Everybody drink up.

Actually, the risk of dehydration is way overblown.

(chuckling)

You're gonna tell me hydrating is bad?

Yeah, right, take a lap.

Oh, I'd never make it all the way around.

In America, we've become obsessed with the dangers of dehydration.

People think that if they're not constantly drinking water,

they risk death.

You're dehydrated.

And you're dehydrated.

And, oh my God, you're practically a mummy.

But that fear is totally baseless.

Yeah, right, bub.

Everyone knows you have to drink eight glasses of water a day.

Yeah, everybody "knows" that, but it's not true.

No study has ever shown or even claimed that.

It's just something people say.

Really?

Now you tell me.

(sarcastic chuckle) Water prevents cramps.

Oh, where'd you hear that?

From my coach.

And I heard it from my coach,

and he heard it from his coach, and so on.

Well, you didn't hear it from science,

'cause science says that ain't true.

Well, how much water am I supposed to drink?

Well, you can just drink when you're thirsty.

That's crazy, you're a crazy person.

Who are you?

Oh, Patty, this is Tamara Hew-Butler.

She's a professor of exercise science at Oakland University.

Our bodies already possess an extremely sensitive measure of dehydration.

It's called thirst.

As long as we drink when we feel thirsty,

we really won't dehydrate.

That's how humans have done it for millions of years,

and it's worked out fine.

The fact is, truly dangerous levels of dehydration

are incredibly rare and only occur in cases

of extreme sickness or isolation.

As long as you have free access to water

and you drink when you're thirsty,

you'll be fine.

Then why do I do this to myself?

Hmm, maybe because beverage companies have spend decades

drowning us in ads like these.

(announcer) Hardworking hydration, keep at it.

Hydrate the hustle.

G2 from Gatorade,

the low-calorie, off-field hydrator.

Lucozade Sport hydrates and fuels you better than water.

'Cause the more water you drink, the better you feel.

Drink more water!

These companies have consistently portrayed dehydration as a serious threat

for one, simple reason -- it gets us to drink more.

The International Bottled Water Association publishes a hydration calculator

that can recommend you drink two liters of water a day.

Dasani tells you that hydration is healthy,

so drink up, preferably Dasani.

Paid spokesman Dustin Pedroia

says he always hydrates with Vita Coco

because it prevents cramps, even though it doesn't.

And in "Runner's World" magazine,

Gatorade ran an ad masquerading as an article titled "Hydration 101."

It included tips like "drink early and often,"

"don't wait until you feel thirsty"

and "always drink sports drinks."

But that's all real science, right?

Ah, here's where it gets sticky.

That ad was sponsored by the Gatorade Sports Science Institute,

which was founded by Gatorade in 1985.

Its scientific mission?

To discover exciting new reasons

people should drink their product.

Our unbiased study found

that people should drink a lot of Gatorade.

Terrific work! Alert the media!

We also may have found a cure for cancer.

Was it Gatorade?

Damn it!

Get back to me when it's Gatorade!

Gatorade also sponsors sports science research at universities across America,

and this can influence their findings.

♪ Money, money... ♪

The American College of Sports Medicine once recommended...

When exercising, you should drink as much as tolerable.

♪ Money, money... ♪

♪ It's all about the money ♪

Other companies soon followed suit.

Evian's parent company founded Hydration for Health,

a group that "promotes healthy hydration habits by sharing scientific research."

Important research, everybody!

Drink Evian!

Science says so.

Oh, I gotta tell the Tots about this.

And, after decades of bad science and marketing,

we now believe dehydration is a dire threat.

Gotta drink, drink or I'll die!

Well, it's not like drinking

too much liquid's gonna kill anybody.

Actually, that's exactly what it can do.

All of this scaremongering over dehydration has created an entirely different problem: overhydration.

Phooey, you drink hard, you pee hard.

Not if you're exercising.

Exercise stops you from peeing

by putting your body in water conservation mode.

And if you overhydrate then,

all that extra fluid has nowhere to go.

Holy crow!

It's called exercise-associated hyponatremia,

and it can be deadly.

In a study of the 2002 Boston Marathon,

nearly one-sixth of the runners studied

were found to have hyponatremia.

These runners drank so much liquid during the race,

that by the finish line, they had actually gained weight.

And she wins by a belly!

Okay, now, that's a joke,

but this is a serious problem in sports.

At least 12 athletes have died from overhydration.

No, that's terrible.

It's true. Overhydration is dangerous.

Most researchers, including myself,

think that it's the marketing of the beverage industry

that's responsibility for this surge

in fluid overload hyponatremia.

So, I've been putting the kids in danger?

No, Patty,

death by hyponatremia is extremely rare.

Just give the kids free access to water.

Let them drink when they're thirsty,

and don't treat these ads as science.

I don't deserve to wear this uniform.

Hey! You made my Patty cry.

Kids, let's practice some tackling drills.

I've got just the dummy.

Ah, no wait!

The truth about concussions is really interesting!