(upbeat Mexican music) - [David] Most of the world's largest cities face water supply problems ranging from challenging to critical.

(singing in foreign language) Mexico city is one of them, and the story goes back 700 years.

(singing in foreign language) (gentle music) - [Narrator] Funding for "In The Americas with David Yetman" was provided by Agnese Haury.

(gentle music) Funding for "In The Americas with David Yetman" was also provided by the Guilford Fund.

(gentle music) (upbeat music) (upbeat Mexican music) - Mexico city is the largest city in the world, or at least one of the three or four largest, with over 20 million people.

It sits at 7000 feet above sea level and is located at the southern end of a basin into which rivers and streams poured for millennia.

There once was, a thousand years ago, an enormous lake here around which civilizations began.

500 years ago, the Aztecs founded their civilization on an island in the lake.

When the Spaniards conquered them, they decided to drain the lake and sent all of the water splashing over into the Gulf of Mexico.

That took away the supply of water for the Mexico City area and 500 years later with the problems of buildings leaning, subsidence, bad quality of water, the planners in Mexico City are trying to figure out how to deliver water to one of the largest cities the world has ever known.

(singing in foreign language) To make sense of that 500 years span, two friends of mine have been joining Mexican experts traveling about the metropolitan area, studying the water history of Mexico city, Stacey Witerfield, an art historian, and Jeff Banister, a geographer.

- [Jeff] So, it looks like we're going to try to shoot down Avenida Chapultepec to try to look at the aqueduct.

- Having a drone to do that is just really important because we can look at all the maps we want and we would never begin to imagine the space that the aqueduct covers here in the center of town, much less from Xochimilco to Chapultepec again.

- [Jeff] The drone can do something that the helicopter can't, which is to have diversity of angles as well as heights, so we can really get a chance to appreciate this potable water system.

- Their historical mapping addresses a critical problem facing the city dwellers, a chronic shortage in the water supply.

(upbeat Mexican music) Nearly half of the residents of Mexico City do not receive a regular water supply.

The alternative to getting water is to rely on what are called (speaks in foreign language), pipe people, who bring water in from trucks, and this is a filling station in these large tank trucks, and drive throughout neighborhoods where water is short.

They provide the water for a fee and the residents thus get their water from the Southern part of the city where Xochimilco used to provide the water.

(upbeat Mexican music) We're on a boat here that goes through a small labyrinth of the Southern end of the Valley of Mexico, and it's used more for recreation, although there are people who live out here, but we have to understand that as late as a hundred years ago, the canal reached all the way down to the central part of the City of Mexico.

- The Chinampas were the pre-Columbian system of agriculture that developed here in the Valley, but they were a form of practicing agriculture over what was a kind of a swampy environment.

Did they dredge up mud from the bottom of the Lake bed and then backfill a staked out area, so that over time, you'd have successive layers of, or mud from the bottom and then you'd farm on top of that, and then ultimately though, that formed the basis of the Aztec City to Tenochtitlan.

That's what the pyramids were built over.

That's what the entire city, the Aztec City, was constructed over, and you see remnants of that today in Xochimilco.

This is actually the last remaining part of the ancient Chinampa system here in Xochimilco and they're still using them.

They're still producing food and ornamental flowers and things here on them.

500 years ago, all of the basin of Mexico was covered by five lakes.

This area is the remnant of that whole system of lakes, and of course, the lakes changed by season.

In the rainy season, they rose, and in the dry season, they kind of, parts of them, sort of disappeared and turned into wetlands.

So, this is a very changing environment that had to be negotiated.

- In 1987, Xochimilco was made a World Heritage Site, but in fact, it was a package deal with Mexico City.

Mexico City was able to thrive and provided citizens with water precisely because it had this beautiful, pure, easily accessible, water supply.

- [Jeff] This is the place that Mexico City drew from to get its potable water starting in the early 20th century.

So, the city's fate became inextricably linked to the Springs and the Lakes of Xochimilco, by 1910.

- What's really interesting here for both of us is this idea of cultural heritage, and the absolute insistence somehow in finding some kind of balance between maintaining this, you know, what the World Heritage Site requires to keep this traditional, and being part of the modern world and how you deal with all of the issues that Xochimilco is confronted with.

- [Jeff] The water sources coming in to Xochimilco have largely dried up.

They're pumping wastewater into it, and so it's very difficult to kind of maintain this human constructed ecosystem.

- [Stacy] And yet it just remains ever present as a destination in Mexico City.

- [Jeff] It's probably maybe a 16th of what it was at the time that Cortes arrived in the Valley of Mexico.

- I mean, here we are surrounded by it and yet if you go up into Mexico City proper, the appearance of water is practically nil in terms of all of its fountains and other heritage sites.

- There's this kind of like back and forth relationship between Mexico's City's political system, the environments that sustain it, and the representations that people make of this environment, and so that long tradition of representing the Valley of Mexico then has really lent itself to creating what is now an incredibly complex water system.

So, a lot of the political tensions you see today are kind of filtered through this long standing story about the City, looking back to what once existed in this Valley.

- [David] As we go through the canals, and see other boats going by, we can try to imagine how the traffic would have been here when this was the breadbasket of the entire Lake civilization.

200000 in Tenochtitlan itself when the Spaniards arrived.

(speaks in foreign language) (upbeat Mexican music) When the water supply from Xochimilco became insufficient, engineer's tapped a nearby river system, (speaks in foreign language) - It's really difficult to imagine the landscape that's shaped by water going 60 kilometers out to Lerma or 30 kilometers to Xochimilco, and so we sort of tried to get some sense of what that actually means.

It's hard to do when the whole city is filled in now, but we walked the entire 30 kilometer aqueduct line from Chapultepec Park to that original source in Xochimilco, and you follow on top of the aqueduct and you see this, sort of the archeology of this water system through the landscape.

- Taking stock of all of the different objects, or kind of an inventory of all the different objects, of water control that were along the way, I'm taking photographs of them, taking GPS plot points, so we're creating maps of the old water system as well.

- This complex here is a part of what is called a breathing station.

This is a breather tube that brought air into the old aqueduct.

If you did not have air put in it, the water would actually slow down and gurgle so much, it would take much longer to get to the end.

This was abandoned when the regular flow from Xochimilco stopped to Mexico City, but the aqueduct is still being used and water comes from time to time, and workers wait here until they get a report there is water and they use these pumps then to transfer the water from here into the tubes that then empty into the big trucks outside.

The water is delivered free to people who otherwise would have no water at all because there's none in their taps.

- [Jeff] Many parts of this water structure are very old, maybe dating to the turn of the 20th century.

It's a constant struggle to maintain the system.

- [David] When you add an earthquake to that, and a lot of the delivery system is made of concrete mains piping, and that's really brittle, so when you get the rocking, it cracked.

It's not like it were PVC or even the old cast iron piping, so add that to the lack of water and the delivery system.

My understanding is that they lose 45% of their water to leakage-- - [Jeff] Which is an astonishing amount of water lost every year to the system.

(upbeat Mexican music) (water splashing) - [Stacy] This is Chapultepec Park, which is almost the size of Central Park.

It's the green space and the lungs of Mexico City.

- [Jeff] What you're seeing here is a temple, a water temple, a monument to the history of water control in Mexico City.

It's marking the place where two old water systems conjoined, one is coming in from the West, from the Lerma, a separate watershed, and another part is coming in from Xochimilco.

These two different sets of architectures bring together two different epics of water control history in Mexico City.

From the air, you're going to see a series of four water tanks that were originally built in the early 20th century.

You're going to see the Carcamo de Dolores, which was finished in 1951, 1952.

The site was meant to be appreciated from the air.

This was Diego Rivera's original idea with the construction of the mosaic fountain.

- What looks like, or has the form of, maybe an ancient Aztec pyramid is actually a modern structure, and underneath that representation is the big aqueduct that brought the water from the real Lerma system about 40 miles away.

It went underneath where I'm standing here and into this building that resembles the Roman Pantheon, where there was an enormous tank where visitors could actually look into and see the water that came from afar into Mexico City.

Now, the water is removed because it was damaging the murals that Diego Rivera painted in the building.

(gentle music) We don't often think of water as having a musical sound, but an electronic expert has managed to convert the sound of the water rushing through the aqueduct, and convert that to an electronic signal and then into music.

So, this is the transcribed sound of the water arriving to Mexico City.

(gentle music) - This mural is called "Water, The Origin of Life", and actually what this would have been is an immensely, kind of, multi sensual experience with the water actually flowing through this tank, and you can even see where the wave lines are that Rivera painted into the walls of the tank, and he paints sort of three tiers of subjects that relate to water in Mexico.

One, more universal, which is the story of evolution.

You can see from the sort of primordial ooze up to complex species, humans.

The next tier shows us effectively the contemporary period with workers who are depicted as contributing to the construction of this whole system, but they also have a very specific personal relationship with people who need water desperately, and you can see they're handing water to an older woman.

There's also people swimming in water.

So, it's very, very personal, kind of one on one relationship.

Then up above, we have something very different.

It's sort of the picture of the state with all of the engineers chose this sort of blueprint or plan of the Lerma Cutzamala system.

- Mexico City was in dire straits leading up to the early part of the 20th century.

Water was scarce in many places.

They were still fighting floods quite frequently, but they really needed a potable water system, and so we have this, so we're standing atop one of these four enormous water tanks and this site is really crucial in the city, not only for its history in terms of providing potable water for Mexico city, dating back to the time of the Aztecs, but also because it's a high point in an otherwise very low - [David] So, they can distribute the water from here, by gravity.

- [Jeff] Exactly.

- What you're looking at here is a very abstract pre-Colombian mask form and it was added to the rim of the tank in the late 20th century.

You can see a very sinuous line of water that encircles the entire tank, actually all four tanks, and is referred to as the Serpent Fountain, and we end up here with this kind of wonderful meeting of the tail of the serpent and the serpent's head right here, which you can see also on all four tanks.

You can also see throughout the city where there are other remains of earlier water systems, the old aqueduct, for example, among others, and they've also landscaped those spaces.

So, there's this kind of creation of sort of water oases, without the water, throughout the city.

- So the city, more than perhaps any other city in the world, except maybe for Venice, did grow up and develop a relationship to its water infrastructure.

60 kilometers away to the West, Mexico City constructed this water system in 1952, one of the biggest in the Western Hemisphere, perhaps one of the biggest in the world at the time, to bring water all the way in from this other river basin.

It really was so focused on sustaining water in the capital city that there was not a whole lot of attention paid to the places that water would be coming from, and that's where Mexico City is today, in the midst of a lot of conflict with these other towns, villages, countryside, places in the countryside, where the water is coming from.

- Many consider this to be the first fountain in Mexico City.

Actually, it is the first fountain that supplied water to the aqueduct that goes through Chapultepec.

It was an important part of the end of the Baroque in new Spain.

The fountain is a symbol of power, the power of the authorities, but now it looks like it does not fit within the landscape of the tall buildings in this part of the city.

(upbeat Mexican music) - This was part of the aqueduct system, the Aztec aqueduct system, that fed into Tenochtitlan into the city center.

So, it was extremely important, here on the edge of Chapultepec Park, which was the primary source of fresh water for the Aztecs, but there's several layers, and what's interesting about this is, it wasn't discovered by archeologists until 1971 when they were digging the big drainage channel.

- So, it lay unused for a few hundred years.

- [Jeff] For several hundred years, yeah, nobody knew it was here.

- [David] Chapultepec Park was part of the Aztecs metropolitan empire.

When their lakes were pumped dry, architects and engineers discovered many unintended consequences.

- The building settled irregularly because beneath them are the remains of Tenochtitlan, the indigenous city.

Where there are pyramids, where there are pre Hispanic structures, the buildings stop sinking.

That is why you see that the palace is raised here, and drops at opposite ends.

There are two factors when considering architecture, the sinking of ground that is on top of a lake and earthquake.

Because of the extraction of water, the ground becomes more breakable and the seismic waves oscillate more.

- As we look at the National Cathedral, it is almost as if it were an optical illusion, but the church is actually splitting in two, and additionally on this side.

That is a result of just subsidence, but if we look at the tower on the right hand side, there is no cross on it.

That is a result of the earthquake of 2017.

We have an example of seismicity and the subsidence caused by drying out of a lake bed, which continues.

In this corner of the circle or the square, you can see the strange configuration of the ground, it's not level, it is jumping all over the place.

Down here, it looks as if it's heading that direction, but that direction, it looks like it's heading this direction.

- This whole thing is tilted down when it would have been level at some point, not that long ago, and 18th century, 17th century, we would have been walking beside a canal by which boats would go into the middle of the city, coming from far South, in the basin of Mexico.

- This would have been a huge market, busy with activity, boats carrying produce and flowers from the South could come in here in a canal, this hill was not there, and bring their produce up across to where the original market of the city of Tenochtitlan lay.

Most flat surfaces, a ball doesn't roll, hello ball, how are you, and now it's going to head out, maybe go all the way to Xochimilco.

(upbeat Mexican music) - This is the shield, the first shield, of Mexico City.

It was given to us by Carlos Quinto, presented here is the idea of the city founded over a lake and the idea of the roads that converge to the city and connect with firm ground.

- I'm standing under a bridge here, it is necessary because the subsidence was such that the bottom is now, it looks to me, at least eight feet below where the original soil was, and it's not the low point.

The low point is probably another foot down here.

In each place, people above are looking down on where the surface used to be, but most dramatic is this church, and we can see the level up here where the surface used to be.

Imagine trying to maintain buildings, or construct new ones, or to maintain a water system in an area with that kind of subsidence, and the danger of earthquakes.

So, I go in here, everything is twisted, everything is askew.

Things are sliding up against the wall because that side of the church is actually falling.

So, the engineers have compensated by adding cables across to hold those two pieces together, and so far, it seems to have worked, but in a big earthquake, I think, maybe the worshipers would get a little bit nervous, I would be.

- The aqueduct is low because of the earthquakes that happened in the city.

It was saved as a monument in the 20th century.

They left some evidence of the most clear examples of how the water formed the city.

The other streets on the shield had the function of connecting the island that was to Tenochtitlan with the firm ground.

What we see here is a street that rises to provide drinking water.

Now, we are bringing water from even farther away.

Today, it is no longer important to leave this symbol that were the fountains, and the remains of the aqueducts with their great commemorative plaques, but for that society, it was very important to make clear that relationship between the formation of the city, the water supply, and those who have political authority over the major construction.

Centuries and centuries of learning to build on marshland, centuries of learning to endure floodings, and the paradox of being on a lake, but always being thirsty because of the lack of potable water.

The architectures, it's deformations, is totally associated with the lake.

The development of this area was possible when the level of the lake began to fall.

Areas that were not on top of the lake were being populated.

Summer, which is a season of major floodings in the city, may no longer be a problem for us, even though now, it is easier to clear up floodings and the other elements we discussed is the effect of the earthquakes within a marshland environment.

Even though the aqueduct is now dry, it's an archeological monument that reminds us of the two determinants of our city.

(upbeat Mexican music) - As is the case with big cities around the world, Mexico City has outgrown its water supply.

It has the additional problem of being located 7000 feet above sea level, and Mexico's big water sources are 6000 feet below, at least.

The sources of Mexico City's water are not as available as they used to be.

The population is growing, the infrastructure is decrepit.

It is a challenge for politicians and for the entire Mexican society to maintain that water, so that every Mexican will have a right to be able to open a tap and get a glass of water.

(upbeat Mexican music) Join us next time In The Americas, with me, David Yetman.

A couple of decades ago, the very mention of the city of Medellin struck terror in the hearts of millions of Colombians and anger through much of the world.

Now, the Medellin region is an international tourist attraction and the city is one of the most vibrant in the Americas.

Yes, things have changed.

550 years ago, we would get on a boat here and if it was full of produce, the kind of things they raised here, how far could we go toward the city?

- [Jeff] Yeah, it's probably about close to 20 miles actually that you could pull your boat into the center of Mexico City.

- [David] And now where do the canals end?

- [Jeff] Not too far outside of Xochimilco.

- [David] So we're pretty close to the limit of how far you can go?

(upbeat music) (gentle music) - [Narrator] Funding for "In The Americas with David Yetman" was provided by Agnese Haury.

(gentle music) Funding for "In The Americas with David Yetman" was also provided by the Guilford Fund.

(gentle music) Copies of this and other episodes of "In The Americas with David Yetman" are available from the Southwest Center.

To order call 1-800-937-8632.

Please mention the episode number and program title.

Please be sure to visit us at InTheAmericas.com or InTheAmericas.org.

(upbeat wind chimes)