Moon water ice reserves may limit future city sizes

A new study suggests that while water ice on the Moon could support small villages or towns for centuries, it may be insufficient to sustain large-scale cities of up to one million people. Researchers Martin Elvis of the Center for Astrophysics | Harvard & Smithsonian and Jonathan McDowell published their findings in Frontiers in Space Technologies, examining the sustainability of lunar settlements.

Estimates suggest the Moon may contain up to one billion tons of water ice, primarily located in permanently shadowed regions (PSRs) near the lunar poles. These cold traps preserve ice that has remained untouched for billions of years. However, even with a highly efficient water recycling rate of 98%—similar to the technology used on the International Space Station—a population of one million residents could exhaust a billion-ton reserve in approximately one century.

Some estimates suggest the actual available water supply could be significantly lower, potentially reducing the lifespan of a small city to just a decade. This resource limitation poses a significant challenge to long-term ambitions for lunar colonization, including plans for heavy industry or permanent human presence on the Moon.