Lunar water reserves insufficient for million-person cities, study finds
Research from the Smithsonian Astrophysical Observatory suggests current water estimates cannot sustain large-scale urban colonization.
The dream of sprawling lunar metropolises may be limited by a fundamental resource bottleneck. A new study suggests that the Moon's available water reserves are insufficient to support large-scale cities, challenging the long-term feasibility of urban-scale colonization.
Published September 14, 2026, in Frontiers in Space Technologies, the research by Dr. Martin Elvis and Dr. Jonathan McDowell of the Smithsonian Astrophysical Observatory analyzes the sustainability of lunar settlements. The scientists found that even the most generous estimates for water reserves in the Moon's permanently shadowed craters—roughly one billion tons—would be depleted far too quickly to support a population of one million people indefinitely.
According to the study, a lunar city of one million inhabitants would exhaust the entire billion-ton reserve in approximately 2.4 years if no recycling were used. Even by applying the 98% recycling efficiency currently utilized by the International Space Station (ISS), the researchers calculate that such a city would only survive for about 100 years before running dry.
The Recycling Gap
To extend the lifespan of a million-person settlement to a millennium, the study indicates that recycling efficiency would need to reach 99.75%. This level of recovery has not been achieved by any current technological system. While energy needs for lunar bases are often viewed as solvable through solar panels on "Peaks of Eternal Light" or nuclear reactors, water is a finite, non-generatable resource that creates a hard ceiling for growth.
Implications for Colonization
These findings cast doubt on the visions of self-sustaining lunar cities promoted by industry figures like Elon Musk and Jeff Bezos. The data suggests a stark divide between the viability of small-scale research outposts—similar to current Antarctic stations—and the leap to urban settlements. While small bases are sustainable, the transition to a city requires either a massive breakthrough in closed-loop recycling technology or the discovery of water deposits significantly larger than current estimates.
Future Outlook
For now, the study positions water as the primary bottleneck for lunar expansion. Future missions will likely need to prioritize more precise mapping of polar ice deposits to determine if larger reserves exist. Until recycling efficiency can be pushed toward the 99.75% threshold, the prospect of a million-person lunar civilization remains mathematically improbable.