How Mexico City can solve its 400-year water crisis

In September 1629, a heavy rainstorm brought water rushing through the streets of Mexico City, and it did not recede. The city had spent the previous 22 years constructing a drainage channel called the Desagüe de Huehuetoca to address a problem that had plagued the city for centuries – finding a place for excess water to go. However, the project was unsuccessful, and parts of the city remained flooded for years, leading to the deaths of more than 30,000 people, primarily from disease caused by standing, sewage-laden water.

Throughout the next four centuries, the city continued to trade its lake for a sinking foundation. The Spanish conquistadors drained Lake Texcoco, where Tenochtitlan had once sat on an island, to prevent flooding. This drainage also eliminated the city's water supply, so engineers began pumping water from the aquifer beneath the old lakebed's soft, clay-rich sediment.

However, this pumping action released pressure on the clay, causing it to compact and the ground to sink. A 2021 study found that subsidence in the worst areas had reached nearly 50 centimeters a year, and the sinking was no longer linked to current pumping rates but rather to decades-old compaction.

This uneven sinking has warped the Gran Canal, causing some sections to be misaligned. To mitigate this issue, engineers now run pumping stations to lift sewage back up to where gravity can take over, effectively repeating the 1607 trade at a greater cost. The Túnel Emisor Oriente, completed in 2019 after 11 years of construction, carries wastewater 62.5 kilometers to Hidalgo state, where it irrigates the Mezquital Valley.

However, only about 36% of Mexico City's wastewater is treated, and the nearby Tula Valley region now draws 90% to 100% of its own aquifer from decades of Mexico City's former runoff.

Most of Mexico City's water is treated properly at the source. However, the system fails once the water leaves the treatment plants, as leaks in the network allow contamination to enter. The city's wastewater network loses roughly 40% of its water, and researchers have documented how contamination can occur through a leaking network, a nearby contaminant source, and a pressure gradient pulling inward.

Rooftop reservoirs, or tinacos, exist because city pressure is not continuous, and a pilot study in Guadalajara found contamination rates more than double when water sits in a home's storage tank compared to water straight from the network.