Musk dreams of a lunar city — but can 1 million people really live on the moon?

Building a city on the moon is no longer the stuff of science fiction. The moon covers about 37.93 million square kilometers — roughly one and a half times the size of North America — and has been called the "eighth continent."

Jeff Bezos, founder of Blue Origin, has argued that heavy industry should be moved off Earth and into space, with the moon as the starting point. Elon Musk, CEO of SpaceX, has said he intends to establish a self-sustaining city on the moon within 10 years.

But a new analysis finds that even assuming a generous estimate of the moon's water reserves and recycling rates on par with the International Space Station, a city of 1 million people would exhaust the moon's water supply within 100 years.

Martin Elvis and Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics recently published their estimates of the electricity and water a lunar city would require in the international journal Frontiers in Space Technologies. The study synthesizes previously published data rather than presenting new observations.

The team calculated that a city of 1 million people on the moon would require about 2.1 gigawatts of electricity. That figure is based on average US household energy consumption, adjusted for the lunar environment — factoring in heating and cooling needs as well as power for agriculture and industry.

The moon's south pole could supply all the electricity a lunar city would need.

Earth's axial tilt of 23.5 degrees causes the sun's angle to vary with the seasons, but the moon's axis tilts only 1.5 degrees, meaning certain spots receive sunlight almost continuously.

Because sunlight arrives at a low angle and never stops, solar panels could be mounted vertically — stacked like walls rather than laid flat. With gravity only one-sixth that of Earth, a solar tower 1 kilometer tall would be structurally feasible on the moon, and earlier research suggests such a tower could generate an average of 3 gigawatts.

The water the team identified as the critical constraint on a lunar city is mostly locked as ice at the bottoms of craters near the moon's poles.

Estimates of how much exists vary widely across studies. The combined estimate for the eight craters considered most likely to contain water is 34 million tons. The team used 1 billion tons — roughly 30 times that figure — as a generous upper bound.

The team calculated that each person living on the moon would need 500 tons of water per year: 125 tons for drinking and hygiene, 2 tons to produce breathable oxygen, and the remainder for growing food.

On the airless moon, oxygen itself must be extracted by splitting water molecules. Without any recycling, a city of 1 million people would exhaust 1 billion tons of water in just two years, the team estimated.

The International Space Station, currently the most water-efficient facility in operation, recycles urine and sweat for reuse and raised its recycling rate to 98 percent in 2023.

Even at that recycling rate, a city of 1 million would run out of water within 100 years. A city of 100,000 could hold out for 1,000 years.

The team concluded that water constraints would limit a long-term lunar population to the hundreds of thousands at most. They also noted that adding showers and laundry facilities — absent from the space station — could actually push recycling rates lower.

Higher recycling efficiency would extend how long a fixed water supply could last, but sustaining 1 million people for 1,000 years would require cutting water loss to one-tenth the rate achieved on the space station.

The team said reaching that level would be difficult, and maintaining it even harder.

Importing water from another celestial body would require about 10 million tons per year for a city of 1 million — enough to demand 27 large landers arriving on the moon every day.

However, most observations to date have probed only a few meters below the surface, leaving open the possibility that additional water could be found at greater depths.

The team said a lunar population of around 1,000 — comparable to the winter crew at an Antarctic research station — could live without water concerns, but managing water for a population exceeding 100,000 would become significantly more challenging.

DOI: 10.3389/frspt.2026.1894104

M. Elvis & J.C. McDowell, "No cities on the Moon: a billion tons of water is not enough for sustainability," Front. Space Technol. 7 (2026) 1894104.