A peer-reviewed study warns that the moon's finite water ice reserves would run dry in as little as two years for a million-person city without recycling, a reality check aimed squarely at SpaceX's ambitious lunar colonization plans.
Astronomers Martin Elvis and Jonathan McDowell published their findings in the journal Frontiers in Space Technologies, and the numbers cut against the grand visions of sprawling lunar metropolises that have dominated space policy conversations in Washington and Silicon Valley alike. Even under the most optimistic water estimates, a large settlement would face hard physical limits that no amount of federal spending or private-sector enthusiasm can wish away.
The study lands at a moment when both NASA and SpaceX are accelerating lunar ambitions. Elon Musk posted on X earlier this year that SpaceX had "already shifted focus to building a self-growing city on the Moon," claiming the company could achieve it in less than ten years. Roughly a month later, NASA laid out plans for a $20 billion moon base that will depend heavily on SpaceX technology. The agency's Artemis IV mission aims to land astronauts near the lunar South Pole as early as 2028.
Elvis, an astronomer at the Smithsonian Astrophysical Observatory, told ABC News that he initially found the water estimates encouraging. The most optimistic projection puts roughly a billion tons of water ice on the moon, mostly locked in permanently shadowed craters near the poles where temperatures never climb above minus 250 degrees Fahrenheit, according to NASA's Jet Propulsion Laboratory.
A billion tons. That would fill Manhattan's Central Park to a depth of nearly 400 feet. It sounds enormous.
Then Elvis ran the numbers on consumption.
"I was very surprised that if you don't do any recycling, then it's about two years for a city of a million people, which is ludicrously short. You couldn't even build the city in that time."
Even with water recycling as efficient as the International Space Station's 98 percent recovery rate, a million-person city would stretch that supply to roughly 100 years. Elvis called that timeline "still not very much, given the investment in building it." And the researchers noted in their report that achieving and maintaining ISS-level recycling on the moon, across an entire city, not a small orbital station, would be "hard to reach and to maintain."
The actual quantity of accessible water ice is almost certainly far less than a billion tons. That figure represents the high end of existing estimates, not a confirmed reserve. Elvis and McDowell did not conduct their own measurements; they used other researchers' projections and modeled what different population sizes would demand.
The researchers drew a clear line in their report between a modest lunar outpost and anything resembling a city. A settlement of about 1,000 people, comparable to the winter population of Antarctica, could use lunar water without much worry. But at 100,000 residents, the math tightens sharply.
"If the settlement remains a 'Moon Village' at a population of about 1,000, comparable to the winter-over population of Antarctica, then we can be relatively carefree in our use of lunar water," Elvis and McDowell wrote. "If the population reaches 100,000, then we need to start being careful."
Power compounds the problem. A city of one million could rely on either solar or nuclear energy, but if the population grew into the millions, nuclear power would become the only viable option. McDowell put it bluntly: "The limits to lunar society are power is really challenging and water is absolutely, limiting."
The study identified several theoretical solutions: more efficient recycling technology, vertical farming, switching settlers to a low- or no-meat diet, importing water from asteroids, and discovering additional lunar water reserves beyond current estimates. None of these are dismissed outright, but none are proven at scale, either. Importing water from asteroids, in particular, remains a concept without a demonstrated supply chain or cost model.
Both the United States and China have robotic missions scheduled for as early as 2027 to search for water ice near the lunar South Pole. Those missions could clarify how much water actually exists and how accessible it is, data that would either validate or further deflate the optimistic projections.
Elvis also raised a geopolitical concern. If lunar water is scarce, who controls it matters. He argued that without cooperation between the United States and China, or between the Artemis partners and rival lunar research station programs, the result would be a race to claim limited resources with no governing framework.
"Without cooperation between China and the U.S. or between the Artemis partners and the lunar research station partners, then the only thing that we have is a free-for-all, and I don't think that's a good solution."
That framing carries its own complications. American taxpayers are being asked to fund a $20 billion moon base. The question of whether those resources, and any water they help extract, should be shared with a strategic competitor like China is a policy debate the study raises but does not resolve.
McDowell said the researchers' goal was straightforward. "There's been so much talk and enthusiasm about a future in which the moon is a part of our civilization and abundantly populated, and science fiction shows with extensive cities on the moon and space traffic around it," he said, "and so we just wanted to, I guess, throw some cold water, literally, on some of that overoptimism."
Elvis insisted the intent was constructive, "not to put a damper on anyone's dreams," but to ground those dreams in physical reality before billions more in public money get committed.
Ambition is fine. But when the taxpayer is writing the checks, the math ought to come before the marketing, not after.
