10,000 Residents: The Calculated Limit for Lunar Water Supply

A new analysis published in Frontiers in Space Technologies suggests that lunar water reserves can sustain a permanent settlement of 10,000 people for centuries, but a million-person city would deplete the supply in approximately 100 years. The study by Martin Elvis and Jonathan McDowell challenges recent public statements about the scale of future lunar habitats. Their work focuses on two essential resources for life support: power and water.

The research follows high-profile claims by space industry leaders. In February, SpaceX CEO Elon Musk stated the company was shifting focus to building a self-growing city on the moon, a project he estimated could be completed in under 10 years. Blue Origin CEO Jeff Bezos has separately claimed that millions of people will live in space by 2045. These assertions prompted Elvis, a senior astrophysicist at Harvard University's Smithsonian Astrophysical Observatory, and McDowell, an honorary professor at the Durham University Space Research Centre, to evaluate the physical constraints of such plans.

The researchers determined that power generation is not a limiting factor. Solar and nuclear sources appear sufficient to support one million people. The constraint lies in water. Current scientific estimates suggest approximately one billion tonnes of water exist on the moon, primarily in permanently shadowed polar regions. Under the assumption that 98 percent of water is recycled, a rate comparable to the International Space Station, a population of one million would exhaust this supply in a century.

Elvis described the total volume as modest, comparing it to an aquarium the size of Central Park filled until the Statue of Liberty is just underwater. He noted that a small lake cannot supply a large city for a long period. A settlement of 10,000 residents, however, would remain sustainable for centuries under the same recycling assumptions. McDowell stated that covering the moon with cities requires finding a way to transport water there, as it is not currently located where large-scale construction is planned.

The authors argue that the one-billion-tonne estimate may be overly optimistic. Elvis suggested the actual amount of recoverable water could be 20 to 30 times smaller than current estimates. He believes only one-third to one-half of present water is accessible, with his best guess being that the usable amount is about one percent of the original figure. This adjustment would reduce the sustainable lifespan of a million-person city from 100 years to one year.

Gordon Osinski, a professor of planetary geology at Western University, noted that satellite measurements carry uncertainties. He believes the water is present but requires ground confirmation. Osinski suggested the water might resemble Arctic permafrost, consisting of sub-millimetre ice crystals mixed into soil that are difficult to extract. The physical form of the ice presents a technical challenge for mining operations.

McDowell emphasized that the findings are not discouraging. He stated that the truth is never negative, and what is negative is attempting a project that is not going to work. The study provides a specific baseline for planners: 10,000 residents is the upper limit for a sustainable lunar town based on currently estimated water reserves.