Study Predicts Lunar Colony's Water Supply Could Last 100 Years

Researchers Martin Elvis from the Smithsonian Astrophysical Observatory and Jonathan C. McDowell from Durham University conducted this study, modeling the longevity of lunar water supplies based on various population sizes. Their estimates rely on the assumption that one billion metric tons of water could be extracted from permanently shadowed regions at the Moon's poles and that this settlement could achieve a recycling efficiency similar to that demonstrated aboard the International Space Station (ISS).

The one billion metric tons figure serves as a generous baseline, rather than an exact measurement of the Moon's available water. Uncertainties remain regarding how much usable water can be extracted, dependent on the ice's location and its integration with lunar soil.

Water resources on the Moon are primarily concentrated in polar regions, especially within craters that have not experienced direct sunlight for approximately 4 billion years. These permanently shadowed areas maintain temperatures below 110 kelvins, enabling the persistence of water ice. Various scientific techniques, including ultraviolet, infrared, radar, and neutron measurements, have been employed to study these deposits, each with distinct limitations regarding depth and efficacy.

Previous analyses have suggested that eight craters in these regions may contain approximately 34 million metric tons of water, though the accuracy of this estimate is debated. The Frontiers researchers stress that while their model uses one billion metric tons to assess population viability and recycling efficiencies, this figure does not equate to confirmed recoverable reserves on the Moon.

Assuming a consumption rate of 500 metric tons of water per person annually—including needs for drinking, hygiene, food production, and respiration—without recycling, a million residents could exhaust the theoretical one billion metric ton supply in about 2.4 years.

The study highlights the pivotal role of recycling in extending the longevity of lunar water supplies. Under a 98% recovery rate, a lunar population of one million could sustain itself for about 100 years. At 99% recycling, this period could extend to 200 years, and at a 99.9% rate, roughly 2,000 years.

Notably, there is a numerical inconsistency in the report regarding the longevity of water supply at 94% recycling, with one part suggesting 33 years for a population of one million, while the text provides an estimate of 40 years. The discrepancy was clarified in relation to a different statistical consideration used in their calculations.

The ISS's current water recycling system demonstrated 98% total water recovery after upgrades in 2023. However, the researchers note that a permanent lunar colony would face unique challenges regarding sanitation and infrastructure, potentially affecting overall recycling efficiency.

With current assumptions, the researchers conclude that water availability may limit the sustainable population on the Moon to a few hundred thousand people unless recycling efficiencies surpass 99.75%.

Enhanced geological mapping of the Moon could refine future water resource assessments, although no new estimates of lunar water reserves have emerged from China’s recently released geological map. This map contains comprehensive information from China's Chang’e exploration efforts but does not quantify accessible water reserves.

The study identifies alternative strategies for extending a lunar colony’s water supply, including improved recycling methods, reduced consumption rates, exploration of additional lunar deposits, and potential imports from other celestial bodies. Agricultural practices, such as vertical farming, are viewed as viable options for minimizing water use in food production.

Ultimately, the one hundred-year projection relies on specific assumptions regarding population, water supply, and recycling efficiency. Key questions remain about the exact quantity and location of water on the Moon and the practicality of its extraction.