Lunar Megacities May Hit a Hard Water Limit Within a Century

The promise of self-sustaining cities on the moon is colliding with a fundamental resource constraint. While major space industry leaders have pitched lunar habitation as a near-term economic and cultural milestone, a new study suggests the celestial body may not hold enough water to support large populations for long. The tension lies between the scale of current ambitions and the physical limits of the lunar environment, specifically the scarcity of a resource essential for life.

The push for lunar development has accelerated in recent years. In February, Elon Musk, CEO of SpaceX, stated on social media that his company was pivoting from Mars settlement to building a self-growing city on the moon. He projected this could happen in under ten years, a faster timeline than the twenty-plus years estimated for Mars. Jeff Bezos, head of Blue Origin, has also voiced optimism, claiming that millions of people could live in space by 2045. These high-profile assertions prompted a closer scientific examination of the underlying logistics.

Martin Elvis, a senior astrophysicist at Harvard University's Smithsonian Astrophysical Observatory, and Jonathan McDowell, an honorary professor at the Durham University Space Research Centre in England, tested these claims against hard data. Their findings, published in the journal Frontiers in Space Technologies, focus on two critical inputs: power and water. The analysis reveals a stark contrast between the two resources, with water emerging as the primary bottleneck for long-term habitation.

Power generation appears manageable. The researchers determined that solar and nuclear sources would be sufficient to sustain a population of one million on the lunar surface. However, the water situation is far less favorable. Most lunar water is believed to reside in permanently shadowed polar regions. Assuming a total reserve of roughly one billion tonnes, which aligns with current estimates, a population of one million could survive for only about 100 years. This projection relies on recycling 98 percent of all water, a rate currently achieved on the International Space Station.

Elvis argues that while one billion tonnes sounds substantial, it is modest in the context of a major city. He compared the volume to an aquarium the size of Central Park filled until the Statue of Liberty is just underwater, noting that it is essentially a small lake that cannot supply a big city for very long. A much smaller settlement of 10,000 people would be sustainable for centuries under the same assumptions, suggesting that current visions of sprawling metropolises may be premature.

The researchers warn that the initial assumptions may be overly generous. Elvis suggests the one billion tonne estimate could be 20 or 30 times too high, and only one-third to one-half of the existing water might be recoverable. His best guess is that the usable amount is about one percent of the original figure, which would shrink the 100-year lifespan to just one year. This highlights the significant risk in planning large-scale infrastructure without confirmed resource data.

There are also uncertainties regarding the physical state of the water. Gordon Osinski, a professor of planetary geology at Western University in London, Ontario, noted that satellite measurements carry uncertainties. He believes the water is present but wants ground confirmation. He suggests it might resemble Arctic permafrost, with sub-millimetre ice crystals mixed into soil, making extraction difficult. Despite these challenges, McDowell emphasized that the findings should not be discouraging. He stated that the truth is never negative, and what is negative is trying to do something that is not going to work.

The study serves as a reality check for the space economy. It suggests that while the moon is a viable destination, the scale and speed of settlement must be carefully calibrated to available resources. Investors and policymakers should consider these logistical constraints when evaluating the long-term viability of lunar commercial ventures.