In 1629, a flood changed the trajectory of what would become the fifth-largest metropolitan area in the world. Modern Mexico City now occupies the once-enormous Lake Texcoco. Nearly 22 million residents of the extended city are facing historic water shortages this year. How did water go from abundant to scarce in this city?

I remember hearing about the Aztec city of Tenochtitlán in my middle school world history class. The famous floating city seemed like the ultimate fort. 

A few years ago, I drove into Mexico City at night; the landscape was vastly different from the images in my history textbook. It was like driving into an indescribably enormous bowl-shaped world. The city of Tenochtitlán was a five-square-mile grid positioned in the center of a lake. Modern Mexico City is a 571-square-mile natural amphitheater that looks as if the entire night sky full of stars is flipped inside out. 

A University of Texas article describes the historic landscape of Tenochtitlán: “Surrounded by lake waters, Tenochtitlán was a perfect example of geographic adaptation, modification and dependence. Throughout the fourteenth and fifteenth [centuries], the [multiethnic] Mexica ‘grew’ the islet through land reclamation. The Indigenous communities that settled in the Valley of Mexico understood that ‘floods were a precondition for a large part of the basin’s agricultural productivity.’” 

They constructed floating agricultural infrastructure to support the local population and adapt to the changing water levels. 

Complex aqueducts transported spring water into the city over the causeways. Similar to the Great Salt Lake in Utah, Lake Texcoco was a dead sea: Water flowing into the lake did not reach the ocean, leading the lake to become increasingly salty as water evaporated. 

National Geographic details the beginning of the shift from water abundance to scarcity: “The Spanish conquistadors, aided by an alliance of Indigenous peoples, laid siege to the Aztec capital for 93 days, until the Mexica surrendered on [Aug.] 13, 1521. A great deal of Tenochtitlán was destroyed in the fighting, or was looted, burned or destroyed after the surrender. The leader of the conquistadors, Hernan Cortés, began the construction of what is now known as Mexico City among the ruins. Lake Texcoco was ultimately drained, and much of Mexico City rests in the lake basin.”

Sinking Buildings

Seasonal flooding became a major problem for the rapidly growing Spanish infrastructure that no longer floated freely on the surface. Construction techniques similar to those in Venice, Italy, were implemented to accommodate the sprawl. The dams and levees constructed in the early 1600s were insufficient to keep the flooding at bay. A massive tunnel was constructed to divert water headed to Tenochtitlán through the nearby mountains. 

The diversion tunnel functioned well for roughly 20 years. In 1629, the city flooded so badly that parts were underwater for five years. A fundamental shift occurred to accommodate the growing population and increase the predictability of water levels: The lake was drained. At the time, it would have been impossible to foresee the magnitude of this decision. 

Modern Mexico City is dry. The flood waters that were undesirable to the Spanish conquistadors are now of vital importance. The population explosion in the city has created a disastrous feedback loop. The groundwater under the city is now a primary source of drinking water, but it is being depleted faster than it can be restored by modern infrastructure. 

The voids left by the groundwater lead to subsidence, causing the buildings to sink. A Wired article projected that parts of the city could sink a foot and a half per year until the structures rest on more solid ground. Over the next 100-150 years, areas throughout the city could drop to 65 feet below the 2019 street level. How do you reliably install potable water lines to a building that could be 6 to 20 inches lower a calendar year later?

$6 Billion in Needed Upgrades

According to a PBS News Hour interview, 40 percent of the water in the Mexico City network is lost to leaks. One of the many factors harming the water delivery system is that the undulating landscape is prone to breaks. Many parts of the city rely on bottled water or tanked delivery to meet daily needs. 

As seen in Cape Town, South Africa, in 2018, there is a possibility of a “day zero” in Mexico City with a complete loss of fresh water citywide. Scientific American notes that the main aqueduct system is depleted, but not empty. However, the upgrades needed to the water grid are estimated to be $6 billion, and they wouldn’t immediately halt the sinking.

Large ocean-side cities, such as Cape Town or San Diego, have the option to desalinate water. It is an energy-intensive option, but it is feasible. Mexico City is about 150 miles away from the Gulf of Mexico and 200 miles away from the Pacific Ocean. Desalinization, tunneling and pumping to the city — which sits more than 7,000 feet above sea level — are not realistic. 

Slow the Shift from Water Abundance to Scarcity

It is easy to assume that the water trajectory of Mexico City is unique. The size of the city is the compounding factor, but other cities could face the same infrastructure woes this century. Population growth outpacing groundwater removal is happening worldwide. Mexico City is experiencing similar issues that Salt Lake City would if it had 22 million residents. 

How can the plumbing community plan to slow the global shifts from water abundance to scarcity? The encouraging aspect is that we have never been better than we are today at efficiently moving water from place to place. Pumping technology is more energy-efficient. Piping connection methods are more efficient and reliable. Water treatment is faster and more consistent. Water metering systems are better at finding leaks and sending alarms. 

Is there enough technology in our collective plumbing system design and installation toolboxes to outpace population growth and groundwater depletion? There is enormous potential to reduce water waste. However, the best water delivery system in the history of Mexico City might have been the aqueducts of the 1500s carrying fresh water into the floating infrastructure of a much smaller city. 

Can even the best plumbing technology of today compensate for a population maximum established by the geography of a city? Is there a network of pipe that could be constructed, with an unlimited budget, to support 22 million people in the bed of Lake Texcoco?