Lunar water budget could sustain a town of 10,000 for centuries, but not a city of a million

Everything in the paper follows from one per-person number. Drinking and hygiene take about 125 tons of water a year on current US usage, and growing that person's food takes another 500, for 625 tons a year per resident ^[2][3][1]. Recycle at 98 percent, the highest recovery rate the International Space Station has achieved, and each resident still needs 12.5 tons of new water a year ^[8][2]. A million residents need 12.5 million tons a year, and a billion-ton reserve covers that for 80 years ^[3]. The authors wrote that a billion tons would not support a population of one million on ISS-level recycling for more than about one century ^[7].

Without recycling, the same million people would draw 625 million tons a year and empty the reserve in 1.6 years, though the paper's text says less than three ^[4][10].

The 30-fold spread between the two reserve estimates decides the ceiling. On the generous billion tons, a town of 10,000 at ISS-level recycling has roughly 8,000 years of water ^[7]. On the more realistic figure the authors cite, about 33 million tons, that same town has about 267 years ^[5][6]. The paper describes several centuries or more for a village of 1,000 and a town of 10,000 ^[9]. Multiply the town by ten and, on the lower reserve, 100,000 people run through the supply in about 27 years ^[8].

"If the lunar population is to grow beyond a hundred thousand," the authors wrote, "water management will be critical and challenging, and we should evaluate the options well in advance" ^[11].

Food is 500 of the 625 tons, so four fifths of gross demand goes to crops ^[9]. The other lever the authors name is recycling: a tenfold improvement takes recovery from 98 percent to 99.8, cuts make-up water to 1.25 tons per person per year, and multiplies every duration above by ten, which would give 100,000 residents about 270 years on the lower reserve ^[10]. They also point to vertical farming and to water imported from asteroids, and note that current surveys reach only a few feet below the surface, so deeper reserves may yet be found ^[16][15].

Energy is the part the study treats as tractable. The rims above the shadowed craters are lit for most of the year and there is silicon on site to make panels ^[13]; Discover's account of the paper suggests that combination could run energy-intensive facilities such as AI data centers near the sunlit peaks ^[14]. That account does not cost the mining of the ice; it stays with consumption rates, recycling efficiency and reserve size.

"Unless recycling can be improved by factors of about 10," the authors wrote, "or a similarly greater water supply is discovered, this result precludes large-scale long-term human habitation of the moon" ^[12].