This post was first published in the newsletter Why Is This Interesting?

One of the first pieces of slang I learned after moving to Mexico City was aguas. Aguas, as in “waters”, plural, does not mean agua, as in “water”, singular. Rather aguas means danger, caution, cuidado wey. The colloquialism dates back a hundred years or more, before the city had indoor plumbing. “Aguas!” someone would yell, quite considerately, as they tossed the contents of their chamber pot out the front door.

The citizens of Mexico City no longer toss their effluvia into the street. Instead, we flush our aguas negras into 6,000 miles of pipes, where it descends northward, beneath the mountains, into Mezquital, another valley. Long ago the farmers there, in their great prescience, negotiated usage rights for the city’s piss and poop. Accordingly, my aguas negras and my neighbor’s aquas negras and the rest of the city’s aguas negras fertilize a great many chili peppers, alfalfa, corn, beans, onions, and other vegetables—which then get sent back to the grocery stores and restaurants of Mexico City where the city’s residents (and flocks of digital nomads) enjoy them in their salads, beginning the cycle anew.

Why is this interesting?

Water has always been a problem in the Valley of Mexico.

Hundreds of years ago, the basin of the valley held an endorheic lake. Water flowed in, but water couldn’t flow out. With no egress, melted snow and rainwater mixed with minerals in the rocky base layer and turned brackish. Result: a shallow lake on top, large aquifer below.

In the 15th century, the residents of Mexico-Tenochtitlan solved this problem by building a system of dikes, flood gates, and spring water aqueducts, separating the salty water from the fresh. In the 16th century, the conquering Spaniards unsolved this problem by destroying the dikes and the flood gates and the aqueducts, spreading disease and pestilence. In the intervening centuries, residents dug increasingly deep wells to tap an increasingly empty aquifer. Finding water to drink has been a problem ever since.

Today, about a third of the city’s water comes from the Cutzamala System, which takes water from the rivers outside the valley and pumps it up and over the mile-high mountains that surround Mexico City. Benefit: water for the city. Detriment: no water for the countryside.

Also a detriment: When people in the countryside lose access to water they move to the city. When more people move to the city, the city needs to pump more water. But 40% of the water coursing beneath the city already leaks into the ground because reasons, and that leakage equals the amount of water used in Houston every year, which is crazy, all of this is all crazy, it’s been crazy for 600 years, it’s all entirely absurd.

Meanwhile, Mexicans lead the world in per capita consumption of bottled water sold by the likes of the Coca-Cola Corporation, Danone, Pepsi, and Nestle, each of whom have been awarded rights to tap (and pollute) Mexico’s waterways. This is what happens when you pave over a lake.

If you happen to be in Mexico City and you’d like to celebrate our (literally) toxic relationship with water, you can make a short pilgrimage to the second section of Chapultepec park to visit a one-room museum called el Cárcamo de Dolores. Opened in 1951, the museum was built to commemorate the entrance of water from the Lerma River to the city. At the time, the museum was a fully-functioning part of the water system where you could watch river water sluice past an immense, partially-submerged Diego Rivera mural. That water eventually damaged the mural, and so was diverted away to restore the (now very beautiful and also very dry) painting. Entrance fee: about a buck fifty.

Just outside the museum, don’t forget to take a gander at Diego Rivera’s monument to Tlaloc, the Aztec god of water. He’s laying down in several inches of filthy water with his head raised, as if to avoid drowning, and his mouth wide open, as if to yell: aguas!