Moon Water Reserves May Cap Cities at 10,000 Residents

Martin Elvis and Jonathan McDowell have calculated a hard limit on how many people can live on the moon based on available water. Their analysis, published in Frontiers in Space Technologies, challenges recent claims by major aerospace executives regarding the scale of future lunar cities. The researchers focused on two critical resources: power and water. While energy generation appears feasible, water availability creates a strict bottleneck for long-term habitation.

The study responds to statements made by industry leaders. In February 2026, Elon Musk stated that SpaceX is shifting focus to build a self-growing city on the moon within ten years. Jeff Bezos has previously predicted that millions of people will live in space by 2045. Elvis, a senior astrophysicist at the Smithsonian Astrophysical Observatory, and McDowell, an honorary professor at Durham University, tested these projections against current scientific estimates of lunar resources.

The findings show that solar and nuclear power can sustain one million people. However, water reserves fall short of that target. The team estimated the moon holds roughly one billion tonnes of water, mostly in permanently shadowed polar regions. Under this assumption, a population of one million would consume the supply in approximately 100 years. This calculation assumes a 98 percent recycling rate, matching the efficiency of the International Space Station.

Elvis described the total water supply as modest. He compared the volume to an aquarium the size of Central Park filled until the Statue of Liberty is submerged. He noted that such a small lake cannot supply a large city for a long period. A settlement of 10,000 people, however, could last for centuries under the same conditions. McDowell stated that covering the moon with cities requires finding a way to transport water to the surface, as it is not currently accessible in bulk.

The researchers acknowledge their estimates may be generous. Elvis suggested the one-billion-tonne figure might be 20 or 30 times too high. He also estimated that only one-third to one-half of existing water is recoverable. His best guess for usable water is about one percent of the original figure, which would reduce the 100-year lifespan for a million people to just one year.

Uncertainty remains regarding the physical state of the lunar ice. Gordon Osinski, a planetary geology professor at Western University, noted that satellite measurements have uncertainties. He believes the water exists but requires on-the-ground confirmation. He described the potential form as similar to Arctic permafrost, with sub-millimetre ice crystals mixed into soil that are difficult to extract. McDowell maintained that the findings should encourage practical planning rather than discourage exploration.

The study provides a quantitative baseline for future mission planning. It suggests that initial lunar settlements should be designed for smaller populations until more water can be extracted or imported. The analysis stands as a factual counterpoint to the rapid expansion timelines proposed by private space companies.