("Koyaaanisqatsi" by Courtney Hartman playing) ♪ Your breath is burning my skin ♪ ♪ Your mouth takes in my water ♪ ♪ And the clouds roll like a river ♪ ♪ The rain falls sharp as ice ♪ ♪ And the oceans tumble over like mist in the night ♪ ♪ And my heart is a machine, a machine keeping time ♪ ♪ And my body is a building scraping at the sky ♪ ♪ And water looks like water running ♪ ♪ Water looks like water running ♪ Funding is provided by The Arthur Vining Davis Foundations, Lynn Bay Dayton and Bruce C. Dayton, Anne Ray Foundation, and viewers like you.

Thank you.

KELLY McEVERS: It's amazing, isn't it?

Our blue planet.

The only planet in the solar system that's surface is covered in liquid water.

♪ ♪ But less than one percent of that is fresh water.

♪ ♪ Drain the salt water away, paint a picture of our freshwater world, and these are the veins that carry the precious lifeblood we all depend on, a liquid with an almost mystical importance to humankind.

♪ ♪ And when you look at our human story through this water lens-- as we have been doing for the past year-- you start to see the extent to which the water molecule has shaped our destiny.

And while our water history is an epic success story, it's also a story of a dangerous dependence with an uncertain ending.

♪ ♪ Because now we face a difficult question: Are we about to become victims of our own success?

♪ ♪ I'm Kelly McEvers, and I'm a radio journalist.

For this story, I've been working with a team of filmmakers and scientists, making a podcast-style documentary, digging deep into how water has shaped and is still shaping our civilization today.

(insects, birds chirping) But one of our crews started the story about as far away from civilization as you can get-- deep inside Africa's Congo River basin, on the trail of a new theory that might explain a critical moment in human evolution.

And that theory is all about water.

♪ ♪ (insects and birds chirping) ♪ ♪ This is a bonobo.

It's a close cousin of the chimpanzee.

You can only find them here in the Congo, and they have this unlikely relationship to water, this rare behavior that gives us a glimpse at how we humans might have taken our very first steps.

♪ ♪ ♪ ♪ So, if we're going to film this, we have to keep up with the bonobos.

And I have to say, this is not easy.

Our crew spent three weeks trying to follow these guys.

(insects and birds chirping) And following Professor Richard Wrangham.

He's our guide to this new theory of how we evolved to walk on two legs.

♪ ♪ Here we are.

Hi, mama.

How are you doing?

She's just sitting looking at us.

She's just fascinated.

"What's this guy doing wading in my pond?"

♪ ♪ You know, it's almost 50 years of walking in the tropical forests of Africa.

Frankly, the thrill never died.

McEVERS: Richard told us that the story of our first steps has always been a hotly debated subject.

Because, up until now, no one can agree how we came to make this move on to two legs, or, in Richard's words, bipedalism.

Bipedalism, which is very frustrating, because this is, in many ways, the defining characteristic of the hominin line, the line that led from the rainforest ape to where we are today.

McEVERS: The generally accepted thinking is that we left the trees and slowly started to walk out onto the savannah.

But it's never been exactly clear how that would have worked.

WRANGHAM: In the initial phases of bipedalism, it would have been hopelessly inefficient.

McEVERS: That is why we're here.

To see an energy efficient way that our tree-dwelling ancestors walked out onto land some six million years ago.

(bonobos and other animals chittering) ♪ ♪ (bonobos and other animals chittering) ♪ ♪ ♪ ♪ So here what we're seeing is the bent-hip, bent-knee locomotion, like Groucho Marx.

You can see her whole body swiveling as she walks.

♪ ♪ McEVERS: Walking like this can be very tiring on land, but it's easy for getting food in water.

WRANGHAM: And that's what's so wonderful about the wading hypothesis.

In the water you're buoyed up, so that the physical stresses are much less.

This is a wonderfully ecological argument for how we became bipedal.

That's what we come from: a water-walking, wading ape.

McEVERS: A water-walking ape might be the missing piece in the puzzle.

And some people go even further, linking water origins to other human attributes like why we sweat or why we lost the hair that covered our bodies, even the size of our brains.

Clearly, for Richard, water was instrumental in the evolution of our uniquely human style of walking.

♪ ♪ And it's this kind of thinking that kept coming up with all the experts we met-- a rethinking of the role of the water molecule in our human story.

♪ ♪ We might take it for granted, but all civilizations are dependent on their supply of fresh water.

Always have been, always will be.

♪ ♪ Of all those experts, for me, water economist Giulio Boccaletti really spelled out how this dependence on water has shaped the world around us.

It's Giulio's first time here.

It is, first time in Cairo.

It's exciting.

It's just an enormous place, with a lot of people, all of them living off one river.

McEVERS: Giulio has spent his adult life trying to convince governments that water scarcity is humanity's biggest threat.

He famously calculated that ten years from now, we will need 40% more fresh water than we will be able to supply.

Not just here in Cairo-- everywhere.

BOCCALETTI: Egypt, in many ways, is a model for the world.

And its management of this one stream of water is essential to the survival of this civilization, and it's true now as it was true 5,000 years ago.

♪ ♪ McEVERS: It is hard to overstate the importance of rivers to the story of our civilization.

It's not just the fresh water that's so important.

Ancient rivers, like the Nile, had a kind of heartbeat-- the pulse of the yearly flood that brought new soil to feed the crops.

Today, the Nile is dammed, but at one time it flooded so far it reached to the pyramids and beyond.

♪ ♪ The waters engulfed areas by up to 40 times the size of the river.

When it receded, it left behind a carpet of fertile soil that fed the world's first great civilization.

♪ ♪ (birds chirping) BOCCALETTI: Ancient Egypt was to the ancient world what the United States has been for the 20th century.

One of the reasons it was so powerful is that, just like the United States today, it was able to provide much, much more food than its population required.

It seemingly didn't have a ceiling of how much it could actually produce.

♪ ♪ McEVERS: And all this food production was the beginning of our addiction to the molecule.

The beginning of a dangerous dependence that made us vulnerable.

Giulio is adamant, when it comes to a water crisis, we have been here before.

♪ ♪ Giulio confessed to me that he only really came to Egypt to walk down this old staircase.

Yeah, I've been waiting to see this for a long time.

This is a nilometer, it's the oldest river gauge in the world, to measure the height of the river.

It's been here for 2,500 years.

McEVERS: The nilometer was used by ancient Egypt's water experts-- the temple priests, the Giulios of the day.

BOCCALETTI: It's sort of strange to think that there was somebody like me worrying about water some four millennia ago, but that's what this indicates.

McEVERS: Each year, the flood would rise up inside the staircase.

The priests would carefully monitor its height using the markings carved into the walls.

BOCCALETTI: A good flood was, at this point, 11 or 12 meters, and yet they were measuring the finger difference or the-the palm difference, or even the-the length of your forearm, the cubit difference.

And so it's an instrument of extraordinary precision, given what they were trying to do.

McEVERS: What they were trying to do was build a predictive model.

This is from ancient Egypt's oldest surviving text, and it is all about water and harvests.

You can see here, you have three cubits, or three forearms-- one, two, three, four, five, six-- six palms, and-and then two fingers.

So here they were recording the height of one year's floods.

McEVERS: By looking into the past, the priests could see into the future.

BOCCALETTI: And that was key, because the success of this instrument as an instrument of prediction depended on having long records.

♪ ♪ McEVERS: Those records could predict a bad harvest, which gave the pharaoh enough warning to distribute food before the famine hit.

It might be a simple stone staircase, but the nilometer's predictive technology was instrumental in Egypt's rise to power.

(birds chirping) BOCCALETTI: This civilization lasted for three millennia; far longer than our western civilization.

And I'm sure that there were times when they were convinced that they would last forever, and they didn't.

McEVERS: Something went wrong.

A water crisis caught up with the pharaohs, and they lost control.

This is the last hieroglyph ever inscribed anywhere in the Egyptian world, and it's defaced.

McEVERS: A last gasp of a civilization that crashed and burned.

An entire civilization ends here.

You know, this is the last sign that the Egyptians left us.

♪ ♪ McEVERS: The reasons for the fall of the empire are, of course, complex.

But Giulio told me about some surprising new research that compares ice-core data from the Arctic with the ancient Egyptian nilometer records.

And there's a direct match between global weather events at the time, the failure of flood waters in the Nile, and the successive collapse of dynasties in ancient Egypt.

It happened time and again, culminating with the fall of Cleopatra.

BOCCALETTI: There were at least two very severe droughts at the end of the Egyptian kingdom during the last reign of Cleopatra.

The droughts persisted for much longer than expected.

And then there would be strife, there would be problems, and the power of the state would be severely weakened.

And that's what happened over and over again during the course of Egyptian history, and in a way, that's what we face today as well.

(vendors shouting in background) McEVERS: We too are vulnerable to changes in the climate.

This is what Giulio's day job is all about, and he wants to warn us, that water scarcity can still lead to famine, social unrest, even war.

♪ ♪ The origins of the world's civilizations... started alongside the fertile banks of four major rivers.

And, like Egypt, none lasted forever.

Their reigns came and went in cycles associated with great droughts or catastrophic floods.

But of the four, only one was defined by its relationship to water.

China is the water kingdom.

♪ ♪ Controlling the molecule is at the heart of this entire civilization.

♪ ♪ Even the word for politics uses the symbol for water.

And at the center of China's mythology is a 4,000-year-old story of a great flood that swamped the land for two decades.

♪ ♪ As legend has it, the people were saved from the flood by a heroic figure known as Yu the Great.

And his ability to tame the Yellow River made him emperor of China's first dynasty, the Xia.

Our water journey took us to the ancient Yellow River valley to meet a man who thinks he's proved this legend to be true.

Wu Qinglong is a geoarchaeologist who has been unraveling this water mystery for the last ten years.

(speaking Mandarin): McEVERS: It's this perilous gorge that hides Wu's evidence of the mythical flood.

♪ ♪ The story begins at an archaeological site called Lajia.

♪ ♪ This is China's Pompeii.

4,000-year-old skeletons, mainly children, perfectly preserved by thick layers of mud and sediment.

WU: McEVERS: This is the first time any western cameras have filmed this amazing find.

And it's hard not to be struck by the scene of devastation.

How these people died is part of Professor Wu's mystery.

WU: McEVERS: The state of the bodies suggests a flood has preserved them.

But the excavation also shows signs of another disaster that might have trapped them first.

WU: ♪ ♪ McEVERS: Inside Jishi Gorge, Wu began to piece together the gruesome chain of events.

His first clue: the signature of a massive earthquake.

WU: McEVERS: An earthquake would explain why many of the skeletons' bones were broken.

But it did not explain how it could have caused the flood that entombed the people.

♪ ♪ McEVERS: The evidence he was looking for was there all along.

It had just been too big to see.

♪ ♪ The remains of an ancient landslide, so big, it once filled the entire gorge and dammed the river behind it.

Wu worked out how, over nine months, the river rose up behind the dam, 600 feet of water, building up, until the pressure got too much.

It burst.

(water crashing) The great flood was real.

♪ ♪ WU: McEVERS: A cataclysmic water event that changed the course of China's history and seeped into the psyche of an entire culture.

And for Professor Wu, it was the culmination of ten years of work.

WU: INTERPRETER: McEVERS: Turns out, China's water obsession was born of real events.

(water rushing loudly) And their struggle to control rivers continued for millennia.

♪ ♪ Many of China's rulers were actually trained as water engineers-- masterminding more and more ambitious projects to bring the molecule under control.

♪ ♪ This 1931 flood, the greatest in living memory, inundated an area the size of New York, New Jersey, and Connecticut combined, leaving four million people dead and 40 million homeless.

♪ ♪ And it was out of this enduring struggle to control the flood that China became masters of the molecule.

Today, the Three Gorges Dam is the monument to that water history.

It is the world's largest hydroelectric project, generating enough power to supply Beijing with all its electricity needs and stopping the floods downstream.

It even has its own boatlift.

♪ ♪ But controlling all this water comes at a cost.

The 400 square miles of reservoir displaced 1.2 million people and caused huge ecological damage.

The loss of habitat caused a dramatic reduction in local rainfall.

And the weight of water... (ship horn blares) has even caused a 30-fold increase in earthquakes here.

Concerned about the environmental impact, scientists use satellite imagery to count the dams across the world and calculate how much water is held behind them.

The water in the Three Gorges, for instance, can be represented by a column 1,000 feet wide... rising over 300 miles high.

And that is just one dam; China has 87,000 of them.

♪ ♪ And it's not only China.

The United States has almost just as many-- 84,000 and counting.

Today, two thirds of the world's major rivers no longer have a connection to the sea, endangering fish populations, wetlands, and estuaries.

Within ten years, 93% of all river water will be choked by a dam.

There is now so much water stored behind dams in the Northern Hemisphere, the weight of the water has tilted the axis of the planet, affecting the speed of its spin.

The way we control water is changing the planet.

♪ ♪ For most of our history, anywhere without fresh water remained off-limits to all but the smallest of settlements.

But there was always another source of water, underground, tantalizingly close, which, if tapped, had the power to change the face of the planet like never before.

(birds chirping) In ancient Mexico, that power of groundwater was connected to the gods.

And today, portals to their underground water world still exist.

(birds chirping) Here, where there is not a lake, river, or stream for hundreds of miles, there are small openings in the jungle called cenotes.

♪ ♪ Sources of water that could support whole cities.

No wonder the Maya attributed a spiritual power to their mysterious underground water source.

(birds chirping) (howler monkey call echoing) CAMILA JABER: Can you hear that?

It's a howler monkey.

McEVERS: Camila Jaber has her own special relationship with the Maya's underwater world.

She's a free diver.

She's actually Mexico's national record holder.

She went down deep... 56 meters, no fins.

McEVERS: On a single breath... Yeah.

McEVERS: For a long time.

It means it's a dive of around two meters... two minutes and 30 seconds, more or less.

Up and down... down and up.

I grew up diving in the cenotes, so I go back very often.

For the Mayan culture, it was a portal to another world where their souls went.

And they were used for sacrifices asking for rain from the gods, and it was a sacred place.

McEVERS: If you want to access this world, you have to dive 200 feet down in a single breath, which is incredible, but that's what free divers do.

And if that wasn't enough, today Camila plans to dive into this eerie toxic cloud at the bottom of the cenote.

Frankly speaking, this is the most worrying thing we can encounter cave diving.

McEVERS: Vincent is accompanying Camila as a safety diver.

ROUQUETTE-CATHALA: This is visually beautiful, but it's pretty toxic, it has exactly the same effect as carbon monoxide.

So it's not really a good thing to be swimming in for ages.

McEVERS: Someone tell that to Camila.

(inhales deeply) ♪ ♪ ♪ ♪ ROUQUETTE-CATHALA: Looks more like dancing in the water than swimming.

I'm not really worried for her, as long as she is not staying very long in the hydrogen sulfide.

♪ ♪ ♪ ♪ JABER: Going through the layer, oh my God, this is so weird because it all goes dark.

You don't know where you are.

It's a very weird feeling because it's just kind of... a cloud.

♪ ♪ And on the way up, you're swimming in this light beam, and it looks like there's something magical happening.

♪ ♪ (birds chirping) McEVERS: It is not surprising the Maya worshiped these natural wells.

For other civilizations it was rare to get such easy access to groundwater like this.

Here in India, this step well has 3,500 steps to access the fresh water below... a long climb to get drink of water.

In this way, for most of our history, underground water was always just out of reach.

That changed in the early 1700s.

Once again, water is at the center of a massive leap in the progress of human civilization.

This time it is all about an invention made on the small, wet island of Britain-- a new machine called the Newcomen engine.

And it harnessed one of the special properties of the molecule, and used steam to drive the first mechanized pump.

Originally designed to get rid of unwanted water from flooded coal mines, soon these pumps would be sucking much desired groundwater all over the world.

♪ ♪ Steam engines powered the Industrial Revolution.

(machines clacking) Steam transported us further and faster.

And that simple, original design for a pump gave us access to groundwater that had been off limits for so long.

(airplane engine drones) There is no better place to see how that has affected the landscape than here in Arizona.

We headed 60 miles east of Phoenix into the desert to see 21st century pumps at work on an unimaginable scale.

M. SANJAYAN: If you just saw this from space and you had no idea about what we do, you'd have a hard time figuring out what this was.

McEVERS: Each one of these circles is watered by a center-pivot irrigator, taps into underground reservoirs that seeped into the earth over tens of thousands of years.

Until we reached them with our really long straws.

M. SANJAYAN: They're just perfect circles, in the middle of nowhere, in the desert... all because we have learnt how to tap water deep underground.

McEVERS: Sanjayan is convinced we have been building a debt here that we will soon have to repay.

And he took us to investigate the extent of our thirst for underground water.

♪ ♪ (plane engine drones) Although it wasn't as easy as we'd hoped.

You would think filming a farming operation wouldn't be that hard.

We called over 50 farms and asked to film on their land.

Not one of them said yes, especially if we were going to mention groundwater.

You couldn't get near this stuff.

It actually says private property right here, no trespassing.

McEVERS: So, we resorted to filming from the side of the road.

SANJAYAN: You had to film it with a drone I had to stand on the edge, and I had to look across a fence.

Don't lose this thing.

(chuckles) M. SANJAYAN: And you think, my God, you know, we've gone around the world and we've filmed all sorts of things that are really sensitive like giant oil rigs or nuclear facilities, and it wasn't this hard.

I mean, it's a piece of farm equipment.

It's not national security, for God's sake.

It's a piece of farm equipment and no one wants to talk to you about it?

That tells you there's something going on.

McEVERS: There is nothing illegal going on here.

But there is an issue... with each of these pumps pulling water out of the ground at up to 3,000 gallons per hour, that is much faster than rainfall replenishes it.

The aquifer can only last so long.

It's kind of amazing.

Look at this water just gushing out.

And it's cold.

Because its coming from deep, deep under the earth.

The last time that water was on the surface, there were mammoths walking around here.

That's crazy!

It's certainly not the most sustainable way of using water.

It might not even be the most efficient way of using water, but it's the fastest way of using water.

And it's hidden water.

It's secret water, it's water that, frankly, not a lot of people want to even talk about it.

McEVERS: Not to us, anyway.

And the reason for all the secrecy?

It's a sensitivity about whose water it is and how long it'll last.

Growing alfalfa is worth half a billion dollars per year in Arizona alone.

That's just been mowed, so that's the alfalfa, what's left of it, that they've now baled.

McEVERS: As long as you own the land, you don't pay for the water underground.

And, while that lasts, no one wants to limit the amount of water they can pump because it means they'll make less money.

Thousands of farms in America are pumping water in this way.

But this farm introduced me to one of the most surprising parts of our water story.

Sanjayan took us here to show us how far some will go to get as close as possible to a water source.

Look at, look at this.

It's incredible infrastructure.

I mean, it's spectacularly built.

Clearly much more money than any of the other farms we've driven by.

I've never seen that kind of infrastructure just to get into a farm, with a big, big gate.

And it looks like a high-secure facility.

Why don't we see if we can get to the very edge of this farm and... and we can just stop there and take a look.

Because they're sure not going to let us in there.

McEVERS: Places like this show us a new way that countries are tapping into each other's water.

M. SANJAYAN: And it's actually owned by a Saudi Arabian company, and you think, "Why is Saudi Arabia in the middle of Arizona?"

McEVERS: So, what's going on?

When you think of the Arabian Peninsula, you think of oil.

But when the Saudis started drilling for oil back in the 1970s, they also found huge reserves of groundwater, enough to fill Lake Erie.

It led to an explosion of center-pivot farms, so big you could see them from space.

♪ ♪ And they got very good at going deep down and sucking that water up at a very fast rate.

In the 1990s, the Saudis were one of the leading exporters of wheat.

McEVERS: They were actually the world's sixth largest exporter.

But that didn't last long.

By 2012, in just 20 years, 80% of their aquifer had been pumped dry.

Almost overnight, they were importing as much wheat as they used to export.

They looked around the world and said, "Where can we grow crops where there is a steady supply of water, where people haven't really caught onto it?"

And guess what, they found it right here in Arizona.

And I think that's this sort of this astonishing story.

McEVERS: What's really astonishing is the extent to which we are all doing this.

The Saudis aren't the only ones tapping into the water of other countries.

In fact, it's going on so much that we're creating a new flow of water around the planet.

One that is not in the form you might expect.

♪ ♪ If you had to name the world's second largest exporter of fruit and vegetables, after the United States, the tiny country of Holland might not be at the top of your list.

But last year alone, their exports were worth $100 billion.

Since medieval times, the Dutch have been the water experts.

And they're still leading by example today.

They recently committed to sustainable agriculture.

And since the year 2000, many farmers have reduced their dependence on water by 90%.

Much of their success lies inside vast arrays of climate-controlled greenhouses.

We ventured inside with water scientist Arjen Hoekstra, and we were blown away by what we saw.

HOEKSTRA: Wow... ♪ ♪ That's impressive.

See all the seedlings?

Young tomato plants.

Hundreds of thousands of those seedlings are growing here.

Outside it is nearly freezing and here inside, it's quite hot here, actually, I must say, but it's everything climate controlled to create perfect conditions for growth.

McEVERS: When you talk to someone like Arjen, you realize he is fascinated by, actually obsessed with, our use of water and its impact around the world.

He even came up with the concept of the water footprint, that measures the amount of water needed to supply our daily needs.

Most people, if they think about water use, they think about their shower, washing their hands or so, or cooking, but in fact, 92% of all the water consumption in the world is related to crop production in agriculture.

McEVERS: 92%.

Just to grow the food that we need to eat.

When you calculate how much water it takes to grow a tomato, it starts to add up.

The interesting thing about a greenhouse like this is that it is kind of a laboratory.

We know the temperature, we know the light, we know exactly how much water the plant needs.

McEVERS: And, if you count every drop, as Arjen has, you discover something quite revealing.

HOEKSTRA: Of all the water that a plant sucks up from the earth, 99% evaporates.

Only one percent is used to build the plant.

But I put it back.

Otherwise you never know what happens.

McEVERS: Inside this greenhouse, the evaporation is contained, and the drip irrigation reduces the water footprint.

Outside, with traditional farming, is 20 times that footprint.

♪ ♪ Worldwide, the average is 200 liters of water for one kilogram of tomatoes.

McEVERS: It takes 26 gallons of water to grow a pound of tomatoes.

So, a tomato's water footprint includes this invisible trail of all the water that was used to make it.

This trail of water Arjen calls virtual water.

♪ ♪ And virtual water is as powerful and important as any flowing river.

You just need someone like Arjen to understand the scale of it.

(ship horn blaring) HOEKSTRA: When I see all those containers, I see water-- a lot of water.

♪ ♪ McEVERS: If a single container ship were filled with tomatoes, and it takes 26 gallons of water to grow a pound of tomatoes, a whole ship like this, has a water footprint of over two billion gallons of virtual water.

That means a container ship filled with green coffee beans, for example, has a trail of over 400 billion gallons of virtual water.

Each boat has a satellite tracker, and mapped from space, you really get to see the scale of this new flow of virtual water around the planet.

Their paths form giant virtual rivers.

Going through the Suez Canal, there is three times more virtual water than real water is flowing over Niagara Falls.

♪ ♪ HOEKSTRA: Water is global resource; if you don't have the water in a country, you can rely on water elsewhere.

McEVERS: This is how Saudi Arabia taps aquifers in America, and causes a virtual water flow from Arizona to Jeddah.

HOEKSTRA: Saudi Arabia, 66% of their total water use is outside the country.

McEVERS: With Europe, it's 44% and the United States, it's 20%.

In other words, this is a global dependency.

This flow of virtual water is humanity's latest innovation to harness fresh water.

Our addiction to the molecule appears to have no limit.

But there is a dark side to virtual water.

Because it pushes the consequences of our thirst for water out of sight and out of mind.

Like our desire for cheap jeans and t-shirts, which sucks a virtual water flow from countries far away.

Take the Aral Sea as an example.

McEVERS: In Uzbekistan, once the fourth largest lake in the world.

But the rivers that flowed into the Aral Sea were diverted to irrigate cotton fields.

HOEKSTRA: The cotton is for export to other parts of the world.

And the rivers don't end up in the sea anymore, the Aral Sea is disappearing.

McEVERS: In just 30 years, the Aral Sea was drained to a desert by the suck of virtual water used to grow cotton.

HOEKSTRA: It's a huge environmental disaster, and that is directly related to that export of cotton.

♪ ♪ McEVERS: Sanjayan witnessed this man-made tragedy for himself.

SANJAYAN: It takes your breath away because it's a gigantic lake, unimaginably big, with ships on it that disappeared in my lifetime-- in my lifetime.

It is too big to almost imagine, that it is humans that have done that.

McEVERS: For Sanjayan, the Aral Sea is just one of many signs.

♪ ♪ The cracks in the system are everywhere, and you don't have to leave America to see them.

Like the Colorado River.

So many dams hold water in their reservoirs, and so many canals siphon it away, that now... You end up with this river petering out, you know, 50 miles before it reaches the sea.

I could stop it with my foot, it had become such a trickle.

McEVERS: Maybe more importantly, our groundwater reserves are at a breaking point.

Sanjayan took us to see the extent of our aquifer depletion.

Here in Arizona, so much water has been pumped from underground, that the ground has dropped and ripped apart.

Holy cow!

Oh, this is unbelievable.

I mean this is like a canyon opening up at my feet.

Now that's... that's a crack.

(laughs) I mean, that's a proper crack in the earth.

Even further cracks down there, be careful!

This is all ready to go.

Whoa, barn owl!

Oh, I'm so sorry!

That's kind of amazing, right?

Because, like, like, nature's found a way to use this little, little bit of geology.

There's barn owls nesting here.

That's the white that I'm seeing here.

This is ridiculous.

It definitely feels like that crack in the wall of your foundations.

McEVERS: And it's not just Arizona.

The ground is sinking in California, New Orleans, Mexico City, Saudi Arabia, Bangkok.

It's a sign.

McEVERS: Shanghai...

It's an absolute sign... McEVERS: Tokyo.... ...that you're running out.

McEVERS: Cracks in the desert, sinking cities, just a few more of the signs that today our demands on fresh water are outstripping supplies.

It's a global problem, one that none of us should feel immune to.

SANJAYAN: And believe me, I'm not above any of this.

If we don't take care of water in a sustainable fashion, it'll be the first environmental tipping point that will bite humans the hardest.

I'm sure of it.

You know, you go around the world looking at places in which people have found ways to reverse ecological trends and come up with things, and I think that...

I mean, I still believe in human ingenuity.

McEVERS: And that does seem to be the question.

Can our ingenuity design a new water future like we've done over and over throughout history?

As we saw in Holland, we can engineer ways of saving water.

♪ ♪ But high tech-solutions can only get so big.

HOEKSTRA: You cannot start growing wheat or rice in those kinds of greenhouses because the amount we consume is so huge, that it would become much too expensive.

McEVERS: For Arjen, it is about a new appreciation of the preciousness of water.

And for Giulio it's just that simple.

All these problems are manageable ultimately, but they certainly won't be managed if we pretend everything can be solved through technology.

McEVERS: It looks like we no longer take our water management seriously enough.

We just don't value it like we used to.

BOCCALETTI: And that's the real risk here, if we believe that we don't actually have to worry because somebody will take care of it, well, that's when the biggest problems arise.

McEVERS: Just like in ancient Egypt, today's temple priests, the scientists, like Giulio, are warning us of a looming crisis.

BOCCALETTI: And I am afraid nobody's listening.

McEVERS: If we don't listen, our dependence on water, this molecule that made us, will be the reason for our undoing.

♪ ♪ For me, this is a wake-up call to start thinking beyond the tap.

And find that deep connection to the molecule that is inside of us all.

Because if the next chapter in our water story is going to be one we survive, our next step needs to be our greatest.

♪ ♪ Next time on "The Molecule that Made Us."

I'm so sorry... McEVERS: Episode three, "Crisis."

ANNOUNCER: Lift off of GRACE-Follow On!

MAN: We have just flat squandered this resource.

To order "H2O: The Molecule That Made Us" on DVD, visit ShopPBS.org or call 1-800-PLAY-PBS.

This program is also available on Amazon Prime Video.

♪ ♪ Follow the story of water at pbs.org/molecule.

♪ ♪ Join the conversation at #MoleculePBS.