Could humanity sustain permanent metropolises on another celestial body? Proposals for building cities on the Moon frequently assume that polar craters contain enough ice to support large populations indefinitely. Private space leaders like Jeff Bezos envision moving heavy industry off Earth, while Elon Musk advocates self-growing settlements on the lunar surface. Yet new calculations by astrophysicists show that even with advanced recycling, a million-person city would exhaust a billion tons of lunar water in roughly a century. [1, 2]
Generating Lunar Power Is the Easy Part
Supplying energy for an extraterrestrial metropolis turns out to be remarkably straightforward. Because the Moon tilts only 1.5 degrees, the Sun circles the polar horizon and rarely sets on elevated crater rims, occasionally called peaks of eternal light [1, 3]. Under the Moon’s weak surface gravity, engineers could erect vertical solar arrays measuring 3,300 feet (1 kilometer) tall, standing roughly 20 percent higher than the Burj Khalifa. Arrays of that height could deliver about 3 gigawatts of electricity [1, 2]. Power is not the obstacle. [1]
Martin Elvis and Jonathan McDowell from the Center for Astrophysics | Harvard & Smithsonian calculated that an urban population fits comfortably within this electrical budget. At peak American household rates, a million residents need roughly 800 megawatts. Farms and industry raise demand to 2.1 gigawatts, still below rim tower generation [1, 2]. Abundant silicon could enable local solar panel manufacturing. Sunny peaks could even power lunar artificial intelligence data centers. [3]
Generating gigawatts of electricity allows a base to operate pumps and lighting without nuclear reactors [3]. Electrical supply will not determine the lifespan of an extraterrestrial population. Solar arrays can deliver continuous current for centuries [1, 2]. Water is far less forgiving. [1]
Where Cities on the Moon Find Ice
Water on the lunar surface survives only in unique geographical refuges. Soon after the Moon formed, asteroid impacts gouged deep craters whose floors have remained shielded from sunlight for roughly four billion years [2, 3]. These depressions form natural cold traps (permanently shadowed crater floors where temperatures stay below 110 Kelvin, or minus 262 degrees Fahrenheit). In that cryogenic cold, water ice deposited by ancient comets and asteroids will not sublimate away into vacuum by more than a millimeter in a billion years. The ice sits locked in eternal dark. [3]
Surveys conducted since 2013 have mapped these shadowed craters, suggesting up to one billion metric tons of accessible water ice, roughly equal to a quarter of a cubic mile [1, 2]. Poured into Central Park, that water would stand 390 feet (120 meters) deep, rising 30 percent taller than the Statue of Liberty [2]. Early research into the Moon’s geological age and early cratering shows how ancient impacts preserved these volatiles in permanent darkness. Yet divided among the complex systems needed to sustain cities on the Moon, a billion tons disappears far faster than enthusiasts expect. [1]
Extracting polar ice allows settlers to obtain drinking supplies, breathable oxygen, and rocket propellant [1, 3]. Lunar cold traps represent the only accessible reservoirs of life-supporting volatiles in the inner solar system. Without local ice, hauling water from Earth would impose prohibitive costs [2, 3]. Those frozen reserves remain strictly finite. [1]
How Human Settlements Consume Polar Water
Every living habitat experiences continuous hydrological drains. An average American uses about 125 metric tons of water annually for personal hygiene, which equals 80 to 100 gallons (300 to 380 liters) each day. Breathing demands two tons per person annually because life-support systems obtain oxygen by splitting water molecules. Comparing these needs with water consumption patterns on Planet Earth reveals that personal hygiene and breathing represent only a small fraction of the total drain. [2]
The overwhelming drain on any closed ecosystem comes from food production. World Bank estimates indicate that growing one person’s daily meals on conventional farms requires 2 to 5 metric tons of water. Elvis and McDowell assumed advanced farming would operate far more conservatively, adopting a baseline of 500 metric tons per person annually. At that rate, an unassisted metropolis of one million people would exhaust a billion tons of water in about two years. [1, 2]
Farming decides the overall drain. Growing food constitutes the single largest water expenditure in any extraterrestrial settlement. Rationing showers cannot alter that mathematical reality [2]. Survival requires radical conservation. [1]
Recycling Limits and the Century Clock
Closed-loop life support has made impressive technological strides in low Earth orbit. The International Space Station currently recovers 98 percent of its water, up from 94 percent before astronauts installed a urine brine processor (a specialized recovery system that extracts residual moisture from wastewater) in 2023. The missing 2 percent loss is where the critical problem emerges. Over successive cycles of consumption and transpiration, that unrecovered fraction steadily siphons water out of the habitat’s closed loops. [1, 2]
That lost margin changes everything. A 2 percent loss rate means a million-person city drains a billion tons of polar ice in roughly a century. [1, 2]
Scaling down the population extends habitat survival proportionally. A smaller community of 100,000 residents operating at space station recycling efficiency could survive on a billion tons of water for roughly 1,000 years. Extending a million-person city to that same thousand-year horizon requires slashing unrecovered losses tenfold, to less than 0.25 percent, an efficiency goal that appears improbable in a municipal environment where plumbing in one-sixth gravity leaks [1, 2]. Elvis told Earth.com in an email that he had assumed a billion tons would prove plenty with recycling, calling the 100-year depletion figure a big surprise. The authors conclude that long-term populations for sustainable cities on the Moon must remain limited to a few hundred thousand people. [1, 2]
Could True Lunar Reserves Be Much Smaller?
All longevity calculations become drastically more pessimistic if initial ice estimates prove overly optimistic. Radar on India’s Chandrayaan-1 orbiter first detected polar ice in 2013, suggesting several hundred million tons. A 2022 review of 65 large shadowed craters estimated that the eight richest hold only 34 million tons combined. Recent optical imaging revealed ice in only 3.5 percent of the coldest traps, though those icy patches contained up to 30 percent ice. The true ice inventory remains uncertain. [2]
If the accessible water supply is 30 times smaller than one billion tons, habitat longevity shrinks by that exact proportion [1, 2]. Under that constrained scenario, a metropolis of one million people exhausts its water in just over three years, while a city of 100,000 residents runs dry within a decade [1, 3]. Overestimating lunar ice reserves creates a catastrophic point of failure for permanent colonization plans. The math leaves no margin for error. [1]
Smaller populations remain viable under these tighter environmental budgets. Elvis noted that a base supporting 1,000 people—comparable to the winter-over research population in Antarctica—could comfortably survive for millennia on available ice. Even an expanded Moon Village housing 10,000 residents could endure for several centuries or more [2, 3]. A community of 10,000 people would represent a major milestone on a world uninhabited for 50 years [2]. Distinguishing between a scientific outpost and full-scale cities on the Moon is essential for realistic mission planning. [1]
Four Strategies to Avoid Running Dry
To bridge the gap between limited lunar ice and long-term settlement goals, Elvis and McDowell outline four theoretical pathways: improving water recovery, cutting agricultural consumption, importing volatiles from space, or discovering undetected ice deposits. Filtration beyond 98 percent efficiency has never operated reliably at municipal scales [1, 2]. Reducing agricultural consumption appears far more promising, with vertical farms demonstrating that crops such as strawberries can grow using 97 percent less water than open-field cultivation. Elvis highlighted vertical farming and lab-grown meat as the most tractable methods for shrinking the human water footprint on the lunar surface. Dietary innovation offers immediate savings. [2]
Importing ice from near-Earth asteroids presents severe operational obstacles. At space station recycling efficiency, maintaining a million-person city on the Moon requires landing approximately 10 million metric tons of imported water each year, which necessitates landing roughly 27 dedicated spacecraft each day. A more practical hope lies in locating hidden reserves beneath the surface [1, 2]. Orbiting neutron detectors sense water only 3 to 7 feet (1 to 2 meters) down, while radar reaches 30 to 65 feet (10 to 20 meters). Loose surface regolith extends dozens of yards deep, potentially sheltering ancient ice pockets that remain invisible to remote sensing. Hidden ice could change the equation. [2, 3]
Confirming whether deeper ice deposits exist will require robotic rovers to drill boreholes into crater floors. A single borehole could settle it. Until core drilling verifies the true depth of polar ice, municipal planning remains dependent on surface estimates. Because accessible volatiles remain strictly limited, Elvis and McDowell stress that lunar polar water must be legally governed rather than exploited on a first-come, first-served basis [1, 2]. International agreements must establish clear resource governance long before permanent cities on the Moon break ground. [1]
- ACADEMIC JOURNAL Elvis, M., & McDowell, J. C. (2026). No cities on the Moon: a billion tons of water is not enough for sustainability. Frontiers in Space Technologies, 7. https://doi.org/10.3389/frspt.2026.1894104 [Article Link]
- ONLINE NEWS Arrais, L., & Ralls, E. (2026, September 14). The Moon may have enough power for a city, but its water may not last. Earth.com. https://www.earth.com/space/moon-city-water-supply/ [Article Link]
- ONLINE NEWS Elvis, M. (2026, September 14). No cities on the moon — there isn’t enough water, scientists say (op-ed). Space.com. https://www.space.com/astronomy/moon/no-cities-on-the-moon-there-isnt-enough-water-scientists-say-op-ed [Article Link]
APA 7: PerEXP Teamworks. (2026, September 15). Why cities on the moon may run out of water in a century. https://perexpteamworks.com/en/cities-on-the-moon-water-limits/
