As Iran’s capital Tehran endures its worst water crisis in living memory, few recent global cases offer clearer lessons than Cape Town in South Africa in 2018.

The city’s narrow escape from “Day Zero” offers a workable blueprint for how Tehran could still avert a breakdown of its own.

President Masoud Pezeshkian underscored the urgency last week with one of the bluntest warnings any Iranian leader has issued: without rain, Tehran may one day have to be evacuated.

Tehran typically receives 50 to 60 millimeters of rain in October and November. This year it has had none, and forecasts offer little hope.

Utility officials have called the shortage “unprecedented,” stressing that the president’s warning is “serious” and that the city “no longer has any water for excess consumption.”

The picture is stark: a megacity entering winter with no meaningful rainfall, groundwater in freefall, and consumption habits far beyond its ecological limits.

How Cape Town pulled back from the brink

Cape Town, a city of four million, endured the worst drought in four centuries beginning in 2015, when winter rains fell to less than half their long-term average for three consecutive years.

By 2018, officials warned of “Day Zero” — the moment when reservoirs would become too low to keep water flowing.

Fear spread quickly: queues for bottled water, soaring tanker prices, and social tension. But instead of losing control, city authorities responded with an unusually disciplined strategy built on strict demand cuts and complete transparency.

• A 50-liter daily limit per person was imposed
• Tariffs rose steeply, with high-use households paying up to ten times more
• A public campaign launched under the slogan “Every Drop Counts”
• Reservoir levels and the projected “Day Zero” date were posted online every day
• Small desalination units, expanded wastewater reuse, and limited groundwater extraction provided backup supply
• Low-income households received additional subsidies to ensure fairness

The impact was dramatic. Water use fell by more than 55 percent in under two years, from 1.2 billion liters per day to about 500 million.When rains finally returned in 2018, the reservoirs refilled. But the deeper lesson endured: transparent, collective action can shift behavior on a massive scale.

High use, high leak

Average household use in Tehran is 250 to 300 liters per person per day — roughly double that of many developed countries. Nearly one third of the city’s water disappears through leaks in its aging network.

Yet policy continues to rely on large-scale water-transfer projects that postpone, rather than resolve, the crisis.

Decades of over-pumping have pushed Tehran’s aquifers into an annual deficit of roughly 130 million cubic meters, with cumulative losses over forty years approaching 5 billion.

Southern districts now face accelerating land subsidence, which Iran’s Geological Survey warns poses “a direct threat” to the city’s infrastructure.

Once aquifers collapse, they cannot be restored.

What can be done?

Cape Town turned fear into a turning point. Tehran has yet to begin that kind of honest conversation. Years of distrust between state and society have made public cooperation far harder to mobilize.

Drawing on Cape Town’s experience, five measures stand out as immediately actionable for Tehran

• Demand before supply: Network repairs, realistic pricing and public education must outrank new transfer projects.
• Transparency builds trust: Citizens need clear, regular data on reservoir levels and consumption.
• Scale up recycling: Treated industrial and domestic wastewater can meet a significant share of demand.
• Protect the vulnerable: Pricing and rationing must account for low-income households to prevent unfair burdens.
• Unify management: Fragmented authority is the biggest obstacle; Tehran needs a single, accountable command structure.

Tehran can avoid a Day Zero with concrete, credible action. The window is still open—but barely, and not for long.