The water was embedded in small glass spheres in the lunar soil where meteorite impacts occur.
These bright, multi-coloured glass spheres were in samples that were collected from the Moon by China in 2020.
Spheres vary in size from the width of a hair to several hairs.
Water content is just a tiny fraction of these, explained Hejiu Hui of Nanjing University, who participated in the research.
As there are billions or trillions of these impact spheres, this could represent substantial amounts of water, but mining them would be difficult, according to the researchers.
“Yes, it will take lots and lots of glass spheres. On the other hand, there are many”, said Hui, in an email reply to the Associated Press (AP).
These spheres could continuously produce water thanks to the constant bombardment of hydrogen by the solar wind.
The findings, published in the journal Nature Geoscience, are based on 32 glass spheres randomly selected from lunar soil recovered by the Chang'e 5 lunar mission.
More samples will be analysed, Hui stressed.
These impact spheres are everywhere, resulting from the cooling of molten material expelled by space rocks hitting the Moon. Water could be extracted by heating the spheres, possibly by future robotic missions.
However, further studies are needed to determine whether this would be feasible and, if so, whether the water would be safe to drink.
This shows that "water can be renewable on the surface of the moon... a new reservoir of water on the moon", added Hui.
Previous studies have found water in glass spheres formed by lunar volcanic activity, based on samples taken by Apollo astronauts more than half a century ago.
These spheres could also provide water not only for use by future crews, but also as fuel for rockets.
The US space agency (NASA) intends to return astronauts to the lunar surface by the end of 2025.
The mission will focus on the south pole, where permanently shadowed craters are believed to be filled with water ice.
New source of water found on the moon
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