---
title: "Cities running out of water: what Tehran, Mexico City and Cape Town show"
description: "Cities running out of water: Tehran, Mexico City and Cape Town came close. What 'Day Zero' means, why aquifers empty and what cities can do."
url: "https://eclair.world/news/cities-running-out-of-water"
lang: "en"
author: "Thierry Gustin"
published: "2026-11-12"
updated: "2026-11-12"
---

# Cities running out of water: what Tehran, Mexico City and Cape Town show

> **Key takeaways** — No major city has completely run dry, but Tehran, Mexico City and Cape Town have come close. Drought is the trigger; the deeper cause is decades of over-pumping, which a UN report now calls "water bankruptcy".

No large city has yet completely run out of water, but several have come within weeks of it. Cape Town nearly shut off taps to four million people in 2018, a key reservoir system serving Mexico City fell to a historic low in 2024, and in November 2025 Iran's president warned that Tehran might have to be evacuated. Drought sets off these crises; the underlying cause is that many cities use more water than rain and rivers can replace.

> **Key points** — About 4 billion people face severe water scarcity for at least one month a year, according to the UN University.  
> Around 70% of the world's major aquifers show long-term decline.  
> Some cities, including Mexico City, are sinking by about 25 cm a year as groundwater is pumped out.  
> Cape Town avoided "Day Zero" in 2018 by cutting use to 50 litres per person per day.

## Which cities have come closest to running out of water?

Tehran is the most recent major city to face the prospect. In early November 2025, President Masoud Pezeshkian said water would have to be rationed if it did not rain by late November, and warned that evacuation might follow if the drought continued, [The New Arab reported](https://www.newarab.com/news/iran-president-warns-tehran-could-be-evacuated-over-water-crisis). Tehran's dam reservoirs had reached their lowest level in 60 years, and the Latyan Dam, one of five key reservoirs, was about 9% full. The city has about 9.1 million residents. We could not find verified reservoir figures for Tehran for late 2026.

Mexico City shows how quickly the picture can change. Its Cutzamala reservoir system hit a historic low of 30% of capacity in June 2024, then refilled to above 97% by November 2025 after heavy rains, according to [Mexico News Daily](https://mexiconewsdaily.com/news/central-mexico-reservoirs-reach-record-high-capacity/). Full reservoirs, however, do not solve the city's deeper problem: its aquifer is being over-pumped, and the ground is sinking.

**Three urban water crises compared**

| City | Low point | What happened next |
| --- | --- | --- |
| Cape Town | Dams at about 13.5% in early 2018 | Day Zero avoided after use was cut to 50 litres per person per day |
| Mexico City | Cutzamala system at 30% in June 2024 | Refilled to above 97% by November 2025; land subsidence continues |
| Tehran | Latyan Dam about 9% full in November 2025 | President warned of rationing and possible evacuation |

## What does "Day Zero" actually mean?

"Day Zero" is the day a city would shut off household taps because supplies have run too low. The term became famous in Cape Town, where officials initially predicted Day Zero for 12 April 2018 after a three-year drought. Supply dams fell to about 13.5% of capacity, and the city limited use first to 87 litres and then to 50 litres per person per day, while raising tariffs and banning outdoor use of groundwater, according to [Engineering News-Record](https://www.enr.com/articles/49733-after-avoiding-day-zero-cape-town-looks-to-bolster-water-system).

Had Day Zero arrived, residents would have been limited to 25 litres a day or less, [National Geographic](https://education.nationalgeographic.org/resource/why-cape-town-running-out-water-and-whos-next/) notes. The city never reached that point. Since then, Cape Town has planned new supply from desalination, groundwater and water recycling, with a combined capacity of 144 million litres a day.

## Why are cities running short of water?

Cities run short because demand has outgrown what nature replenishes, and drought exposes the gap. A [UN University report published on 20 January 2026](https://unu.edu/inweh/news/world-enters-era-of-global-water-bankruptcy) argues that much of the world has moved beyond a temporary "crisis" into "water bankruptcy", meaning withdrawals have exceeded natural limits for so long that some losses cannot be reversed. Its key findings:

- About 70% of major aquifers show long-term decline.
- About half of the world's large lakes have lost water since the early 1990s.
- About 2 billion people live on sinking ground, and some cities are subsiding by about 25 cm a year.
- About 4 billion people face severe water scarcity for at least one month a year.
- About 2.2 billion people lack safely managed drinking water.

Mexico City is a textbook case of subsidence: land there is sinking by about 25 centimetres a year, [the UN University explains](https://unu.edu/inweh/article/world-water-bankruptcy-un-scientists-report-heres-what-means). Once compacted, the pores in an aquifer cannot simply be refilled. Earlier analysis by the [World Resources Institute](https://www.wri.org/insights/highest-water-stressed-countries) found that 25 countries, home to a quarter of the world's population, face extremely high water stress every year, and that an additional 1 billion people are expected to live with extremely high water stress by 2050.

## Does a wet year end the crisis?

A wet year refills reservoirs but rarely restores groundwater. Mexico City's 2025 recovery shows the difference: surface reservoirs filled up within a season, while the aquifer beneath the city continues to sink. Climate change adds to the pressure on supplies, a theme we explore in our explainer on [the first year above 1.5C](https://eclair.world/news/first-year-above-1-5c). Drought can disrupt trade too: low water in Gatun Lake forced the Panama Canal to restrict shipping in 2023 and 2024, as we explain in [how shipping chokepoints affect prices](https://eclair.world/news/shipping-chokepoints-prices).

> Bankruptcy management requires honesty, courage, and political will.
>
> — Kaveh Madani, director of UNU-INWEH, 20 January 2026

## What can cities do to avoid running dry?

The most effective short-term tool is cutting demand, as Cape Town showed. Over the longer term, cities are diversifying supply and protecting groundwater. The main options are:

1. **Demand limits and pricing**, such as Cape Town's 50-litre limit and higher tariffs for heavy users.
2. **New sources**, including desalination for coastal cities and recycled wastewater.
3. **Aquifer management**, limiting pumping so groundwater levels can stabilise.
4. **Rethinking irrigation**, since more than 40% of irrigation water comes from aquifers that are being drained, according to the UN University.
5. **Early warning**, so restrictions start before reservoirs reach single digits.

## Frequently asked questions

### Has any major city ever completely run out of water?

No major city has fully turned off household taps for its whole population. Cape Town came closest in 2018, when officials planned a "Day Zero" for April that year, but strict limits of 50 litres per person per day, higher tariffs and other measures pushed the date back, and it never arrived. Tehran faced a similar warning in November 2025.

### What was Day Zero in Cape Town?

Day Zero was the date on which Cape Town would have shut off household taps, leaving residents with 25 litres of water a day or less. It was first predicted for 12 April 2018. The city avoided it by cutting use sharply, with a limit of 50 litres per person per day.

### What is water bankruptcy?

Water bankruptcy is a term used in a UN University report published in January 2026. It describes places where people have taken more water than rivers, lakes and aquifers can replace for so long that some of the damage cannot be undone, for example when over-pumped aquifers collapse and the land above them sinks.

### Why is Mexico City sinking?

Mexico City is sinking because groundwater is pumped from the aquifer beneath it faster than it is replenished. As the water is removed, the clay and soil compact and the ground drops, by about 25 centimetres a year in parts of the city according to the UN University. Compacted layers cannot be refilled, so the damage is largely permanent.

## Sources

- [UN University (UNU-INWEH) — World enters era of global water bankruptcy](https://unu.edu/inweh/news/world-enters-era-of-global-water-bankruptcy) (20 January 2026)
- [UN University — World water bankruptcy: UN scientists report, here's what it means](https://unu.edu/inweh/article/world-water-bankruptcy-un-scientists-report-heres-what-means) (2026)
- [World Resources Institute — 25 countries, housing one-quarter of the population, face extremely high water stress](https://www.wri.org/insights/highest-water-stressed-countries) (16 August 2023)
- [The New Arab — Tehran faces water rationing and evacuations if no rain soon, president warns](https://www.newarab.com/news/iran-president-warns-tehran-could-be-evacuated-over-water-crisis) (7 November 2025)
- [Mexico News Daily — Central Mexico reservoirs start November at nearly 100% full](https://mexiconewsdaily.com/news/central-mexico-reservoirs-reach-record-high-capacity/) (6 November 2025)
- [Engineering News-Record — After avoiding 'Day Zero', Cape Town looks to bolster water system](https://www.enr.com/articles/49733-after-avoiding-day-zero-cape-town-looks-to-bolster-water-system) (17 July 2020)
- [National Geographic Education — How Cape Town avoided Day Zero, and what we can learn](https://education.nationalgeographic.org/resource/why-cape-town-running-out-water-and-whos-next/)

— Thierry Gustin, Editor-in-chief · November 12, 2026