Water Constraints Could Limit Future Moon Population, Scientists Say

The prospect of life on the moon has captivated people for generations. From scientific studies to science-fiction epics, visions of sprawling lunar cities and permanent settlements have long fueled hopes that Earth’s nearest neighbor could one day become a new frontier for humanity.

That dream has recently gained fresh momentum. In February, SpaceX founder and CEO Elon Musk wrote on X that the company had redirected its attention toward creating a self-expanding city on the moon, suggesting it could be possible within a decade, compared with more than 20 years for Mars. The following month, NASA detailed its own vision for a $20 billion lunar base, a project expected to rely substantially on SpaceX technology.

However, a newly released study suggests that the biggest plans for a moon city could face hard limits. Researchers say restricted water supplies and the immense energy needed to keep a large population alive may make a vast lunar settlement far more difficult than supporters envision.

The report, published Monday in the journal Frontiers in Space Technologies, was led by Smithsonian Astrophysical Observatory astronomer Martin Elvis and astrophysicist Jonathan McDowell, a space sustainability specialist. Using estimates of the moon’s available water, the pair examined how large a lunar city might realistically become, how long it could remain operational and what it would take to provide enough power for its residents.

“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, and so we just wanted to, I guess, throw some cold water, literally, on some of that overoptimism,” McDowell told ABC News.

McDowell said he expects humans will ultimately establish outposts on the moon. Still, he cautioned that the physical realities of the lunar environment will place a ceiling on the scale of any future moon society.

Much of the moon’s known water ice is thought to be locked inside permanently shadowed regions near its poles. These craters receive no sunlight and can remain colder than minus 250 degrees Fahrenheit, according to NASA’s Jet Propulsion Laboratory. NASA’s Artemis IV mission is targeting a crewed landing near the lunar South Pole as soon as 2028, while the U.S. and China are planning robotic missions that could begin searching the area for ice as early as next year.

“I’ve been looking at places to put astronomical telescopes on the moon, and one of the favorite places are these permanently shadowed regions,” Elvis told ABC News. “So, I got to look at the amount of water that was there, and at first I was very impressed, because the first estimates were going on towards a billion tons, and that sounded like a lot. But then I got to thinking about how there’s no such thing as perfect recycling. So, how much would you lose? How long will that last?”

Drawing on water-ice estimates from earlier research, Elvis and McDowell noted that the widely cited figure of 1 billion tons represents an optimistic upper-end scenario; the true supply could be considerably lower. Even at that level—an amount they say could cover Manhattan’s Central Park to a depth of almost 400 feet—the researchers concluded it would not support a major long-term lunar settlement.

“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,” Elvis said.

Elvis says that if a lunar city of a million people could recycle water with the same efficiency as the International Space Station, with its 98% recovery rate, that would give the city at least 100 years of water.

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“That’s still not very much, given the investment in building it,” said Elvis.

While a large city may not be realistic, Elvis and McDowell say that doesn’t mean humans can’t live and work on the moon for a long time and achieve important scientific discoveries.

“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,” they wrote in their report. “If the population reaches 100,000, then we need to start being careful.”

The scientists say there are potential ways to overcome the limited water supply and build larger cities on the moon.

More efficient recycling could extend the lifespan of a million-person city, although they say “that goal will be hard to reach and to maintain.” The duo says techniques like vertical farming and switching to a low- or no-meat diet could reduce water use. They say water could also be imported from other places, such as an asteroid. And while their estimate of a billion tons of water is much higher than what’s believed to exist, Elvis and McDowell say finding additional water could extend a large city’s lifespan.

“The limits to lunar society are power is really challenging and water is absolutely, limiting,” said McDowell.

Elvis says the goal of the research is not “to put a damper on anyone’s dreams” but to provide a reality check about the challenges of building large lunar settlements. He says he hopes that their analysis will encourage people to ask questions about what’s possible and come up with solutions.

Elvis and McDowell are also encouraging countries to cooperate in managing the moon’s limited water resources, rather than trying to secure what water exists for themselves.

“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,” said Elvis.