Mexico City and its nearly 22 million residents are on the brink of a severe water shortage.

The city’s water crisis is driven by a combination of geographical issues, rapid urbanisation, leaky infrastructure, and the exacerbating effects of climate change. 

Recent years have seen abnormally low rainfall, extended dry spells, and rising temperatures, placing significant stress on the water system, which is struggling to meet the growing demand. 

As a result, authorities are having to implement strict restrictions on water drawn from reservoirs.

“Several neighbourhoods have suffered from a lack of water for weeks, and there are still four months left for the rains to start,” Christian Domínguez Sarmiento, an atmospheric scientist at the National Autonomous University of Mexico (UNAM), recently told reporters.

Although political leaders have attempted to downplay the severity of the situation, some experts believe that Mexico City could face “day zero” within months, a scenario where large areas of the city would be without running water.

Mexico City, situated on a high-altitude lake bed at around 7,300 feet above sea level, is built on clay-rich soil, making it vulnerable to earthquakes and climate change impacts. 

The Spanish conquest of the Aztec city in the early 16th century led to the drainage of the lakebed and replacement of canals and forests with concrete and asphalt, setting the stage for modern-day issues of flooding and water scarcity.

Today, about 60 per cent of the city’s water comes from its underground aquifer, which has been over-extracted, causing the city to sink at a rate of approximately 50 centimetres per year. 

The aquifer’s depletion is exacerbated by impermeable surfaces that prevent rainwater from replenishing it. The remaining 40 per cent of the city's water is pumped from sources outside the city, with around 40 per cent lost to leaks during the inefficient transportation process.

The Cutzamala water system, providing about 25 per cent of the Valley of Mexico's water, is currently at historic lows, operating at around 39 per cent capacity due to severe drought. 

“It’s almost half of the amount of water that we should have,” says Fabiola Sosa-Rodríguez, head of economic growth and environment at the Metropolitan Autonomous University in Mexico City.

In October, Mexican water commission Conagua announced an 8 per cent reduction in water from Cutzamala to ensure the supply of drinking water during the severe drought. Subsequent weeks saw further restrictions, reducing water supply by nearly 25 per cent. The authorities are now working on measures to distribute the water that Cutzamala has over time, to ensure that it does not run out.

Approximately 60 per cent of Mexico is experiencing moderate to exceptional drought, with nearly 90 per cent of Mexico City in severe drought conditions, expected to worsen until the rainy season begins in a few months. 

Natural climate variability, including the recent shift from La Niña to El Niño, has contributed to the drought and inadequate rainy seasons. 

However, long-term human-caused global warming has intensified these conditions, leading to prolonged droughts, extreme heat waves, and heavier rains when they do occur.

The potential for a ‘day zero’ where the city’s taps run dry looms large. 

Some local media have reported that without significant rain, day zero could arrive as early as June 26. However, government officials, including President Andrés Manuel López Obrador and Mexico City Mayor Martí Batres Guadarrama, have dismissed these claims as “fake news”.

Conagua is currently undertaking a three-year project to enhance water infrastructure, including new wells and water treatment plants, to cope with reductions in the Cutzamala system.

The unequal distribution of water in Mexico City remains a significant issue. Wealthier areas often remain unaffected by shortages, while others, like the Tlalpan district, suffer severe shortages. 

Poorer residents are having to fork out exorbitant amounts for water delivered by truck, and sometimes endure weeks without water. 

The water crisis in Mexico City mirrors challenges faced by other major cities worldwide, such as Cape Town, South Africa, which narrowly avoided a "day zero" in 2018 through extreme conservation measures and luck. 

To avoid such crises, experts recommend diversifying water sources, improving infrastructure, and implementing sustainable solutions. While some strategies, like desalination, may not be feasible for Mexico City due to high costs, significant investment in infrastructure and conservation efforts are critical for long-term resilience.

Advocates are calling for improved wastewater treatment, rainwater harvesting systems, and fixing leaks to increase water efficiency and reduce reliance on the over-extracted aquifer.