Scientists analyzing lunar water reserves conclude that while the moon's polar ice could support small settlements, a million-person city would exhaust available water in just over a century even with 98% recycling efficiency. Though solar power generation is feasible at the lunar poles, water scarcity presents the primary constraint to large-scale lunar habitation.
Scientists conclude that lunar cities are not sustainable due to insufficient water reserves. Even with optimistic estimates of one billion tons of water and 98% recycling efficiency, a city of one million people would exhaust supplies in about 100 years, while realistic estimates suggest much faster depletion.