Researchers calculate Moon has too little accessible water to support a million-person city

# Summary Astronomers Martin Elvis and Jonathan McDowell examined how much water and power would be required to support hypothetical lunar populations. Their calculations show that powering a large lunar city is technically plausible with solar infrastructure, but water is the hard constraint. Known polar ice deposits—even at optimistic totals—cannot reliably sustain million-person cities without major gains in water recycling or finding new supplies.

# Power outlook Elvis and McDowell estimate that the Moon can supply significant electrical power. They propose kilometre-tall towers covered in photovoltaic arrays that could generate on the order of 3 GW of electricity. The Moon's surface contains large amounts of silicon, so manufacturing solar panels in situ is considered feasible. The authors judge that nuclear power would not be necessary to meet energy demands for even large settlements if photovoltaic production and deployment are achieved.

# Water is the limiting factor

• With water recycling at about 98% (comparable to the International Space Station), a population of 1,000,000 would have enough water for roughly a century before the supply runs out.
• To sustain a 1,000,000-person city indefinitely would require recycling efficiencies better than about 99.5%, major reductions in per-person water use (for example via vertical farming or other techniques), or discovering substantially more water on the Moon.

# Practical settlement scales today Given the current estimates of polar ice and achievable recycling tech, the authors conclude that small towns are the realistic near-term option. A settlement on the order of 10,000 people could be sustained for several centuries without needing breakthroughs in recycling or resource discovery. Larger settlements become progressively harder to maintain because each percentage point of additional loss in recycling multiplies total consumption over time.

# What this means for planners and policymakers

• Investment in improved water-recycling systems beyond 98% yields disproportionate benefits if planners aim for populations in the hundreds of thousands or more.
• Prospecting for additional water at the poles or elsewhere on the Moon remains a strategic necessity for any program that targets large-scale permanent habitation.

# Bottom line Photovoltaic power and in-situ manufacturing make energy a solvable problem for substantial lunar populations. Available polar ice and current recycling technology, however, limit sustainable population sizes: towns of tens of thousands are plausible for centuries, while million-person cities would require either much better recycling, radical water-use reductions, or finding far more lunar water than current maps indicate.