Water reserves on the Moon may be insufficient not only to sustain large settlements but even for their construction, ABC reports.

Astronomer Martin Elvis of the Smithsonian Astrophysical Observatory (USA) and astrophysicist Jonathan McDowell have calculated that, under the most optimistic scenario, a city of one million people would exhaust its water supplies in approximately two years without water recycling.

Even with the 98% recycling efficiency currently employed on the ISS, the water supply would last only 100 years. Scientists suggest that lunar water could be used relatively freely if the settlement remains a "lunar village" with a population of around a thousand—comparable to the overwintering population of Antarctica. However, if the population were to grow to 100 thousand, water conservation measures would be required.