Moon water is too scarce to sustain cities, scientists warn

A hard limit on lunar life

The dream of building bustling cities on the moon has hit a hydrological wall. While space billionaires and government agencies have envisioned lunar metropolises housing up to a million people, a new analysis shows that the moon simply does not have enough water to keep them alive.

According to a study published in the journal Frontiers in Space Technologies, even the most optimistic estimates of lunar water would sustain a city of one million people for just over a century. If more realistic, recent estimates of the moon's ice reserves are correct, that lifespan shrinks to just a decade.

The calculations, performed by astrophysicists Dr Martin Elvis and Dr Jonathan McDowell, cast a cold shadow over the grand plans of space entrepreneurs. Jeff Bezos has spoken of moving heavy industry to the moon, and Elon Musk has proposed "self-growing cities". But Elvis and McDowell warn that while energy is plentiful, water is a hard, unforgiving limit.

Abundant power, empty taps

Generating electricity is actually the easy part. The study found that solar arrays mounted on kilometre-high towers, built on the permanently sunlit rims of polar craters, could generate three gigawatts of power. Silicon is abundant in the lunar dust, meaning solar panels could eventually be manufactured on-site to run everything from mining operations to AI data centres.

The water, however, is locked away in the freezing, pitch-black floors of polar craters where temperatures stay below 110 Kelvin (minus 163 degrees Celsius). Since 2013, orbital missions have mapped these "cold traps", suggesting they contain up to one billion tonnes of water ice delivered by ancient asteroid impacts.

That sounds like a lot, but human cities are incredibly thirsty. Even if a lunar city recycled its water with 98 per cent efficiency—the standard currently achieved on the International Space Station—a population of one million would quickly run dry. When adjusted for newer measurements suggesting there is actually 30 times less water than previously hoped, the timeline becomes critical. A large city would exhaust its resources in about ten years.

What happens next

Smaller colonies, however, remain highly viable. The researchers found that a village of 1,000 people or a town of 10,000 could comfortably survive for several centuries under the same conditions.

To build anything larger, future colonists would need to look elsewhere. The authors suggest that fivefold improvements in recycling, vertical farming, or towing water-bearing asteroids to the moon could bridge the gap. Alternatively, vast deposits of ice might lie deeper than the first few metres of surface rubble that current sensors can detect. Until those deeper reserves are found, the grand lunar city remains a mirage.