Water scarcity confines lunar cities to small towns
New research indicates that while power is sufficient for a million people, the Moon's limited water reserves would sustain that population for only one century.
By Aiko Soto ·
A million lunar residents could exhaust the Moon's available water within a single century, according to a new analysis published in Frontiers in Space Technologies. The study challenges optimistic timelines for large-scale human settlement proposed by major aerospace leaders. It suggests that while energy infrastructure can support massive populations, the physical limits of water availability are far more restrictive.
SpaceX CEO Elon Musk stated in February that his company is prioritizing a "self-growing city on the moon" over Mars, aiming to achieve this in under ten years. Blue Origin CEO Jeff Bezos has separately predicted that millions of people will live in space by 2045. 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, examined these claims. Their work focuses on the dual requirements of power and water for long-term survival.
The researchers determined that power generation is not the primary barrier. Solar and nuclear sources appear capable of sustaining one million people on the lunar surface. Water presents a much tighter constraint. Current estimates place the total water supply at approximately one billion tonnes, mostly located in permanently shadowed polar regions. If a population of one million recycled 98 percent of its water, matching the efficiency of the International Space Station, that supply would last only about 100 years.
Elvis compared the total water volume to an aquarium the size of Central Park filled until the Statue of Liberty was just underwater. He described the reserve as a "small lake" that cannot supply a large city for long. A settlement of 10,000 people, however, could remain sustainable for centuries under the same assumptions. McDowell noted that covering the Moon with cities, as depicted in science fiction, requires finding new water sources because the existing supply is insufficient for that scale.
The researchers' baseline figures may be optimistic. Elvis estimated that the one-billion-tonne figure could be 20 or 30 times too large. He suggested that only one-third to one-half of the water is likely recoverable. His best guess places the countable water at about one percent of the original estimate, which would reduce the sustainable timeframe for one million people from 100 years to just one. Gordon Osinski, a professor of planetary geology at Western University, added that satellite measurements carry uncertainties. He compared the potential ice formations to Arctic permafrost, noting that sub-millimetre crystals mixed into soil make extraction difficult.
McDowell emphasized that the findings clarify engineering goals rather than ending the effort. He stated that the truth is never negative and that it is more problematic to attempt projects that are destined to fail. The study provides a concrete baseline for future mission planners regarding the maximum population size the Moon can support with current knowledge of its resources.
