Lunar Water Reserves: Harvard Study Caps Moon Cities at 10,000 Residents

Researchers at Harvard University and Durham University determined that lunar water reserves are insufficient to support cities of one million people for extended periods. Their analysis, published in the journal Frontiers in Space Technologies, suggests that a population of 10,000 residents can be sustained for centuries using currently estimated ice deposits.

The study responds to public statements by major aerospace executives regarding rapid lunar colonization. In February, SpaceX CEO Elon Musk announced a shift in focus toward building a self-growing city on the moon, predicting a timeline of under 10 years. Blue Origin CEO Jeff Bezos has similarly claimed that millions of people will live in space by 2045. Martin Elvis, a senior astrophysicist at the Smithsonian Astrophysical Observatory, and Jonathan McDowell, an honorary professor at the Durham University Space Research Centre, tested these claims against available data on power and water.

Power generation was identified as the less restrictive factor. Solar and nuclear sources appear capable of sustaining one million people. Water, however, presents a sharper constraint. Current estimates place lunar ice reserves at approximately one billion tonnes, primarily located in permanently shadowed polar regions. Under the assumption that 98 percent of water is recycled, a rate consistent with International Space Station protocols, one million residents would deplete these supplies in roughly 100 years.

Elvis characterized the total water volume as modest in comparison to terrestrial features. He compared the supply to an aquarium the size of Central Park filled until the Statue of Liberty is submerged. He noted that such a volume is comparable to a small lake, which cannot supply a large city for a long duration. McDowell added that covering the moon with cities as depicted in science fiction requires new methods to transport water to the surface, as existing reserves are limited.

The authors noted that their baseline estimate of one billion tonnes may be optimistic. Elvis suggested the actual recoverable amount could be 20 or 30 times smaller, potentially reducing the 100-year sustainability window for a million-person city to a single year. Gordon Osinski, a planetary geology professor at Western University, highlighted uncertainties in satellite measurements. He proposed that the ice may exist in a form similar to Arctic permafrost, with sub-millimetre crystals mixed into soil that are difficult to extract.

McDowell emphasized that the findings clarify engineering constraints rather than negate the goal of lunar settlement. He stated that the truth of the resource limitations is not negative, whereas attempting projects that exceed those limits is. The study provides a baseline for future infrastructure planning based on currently recoverable water volumes.