India’s Chandrayaan-1 probe detected water by mapping wavelengths of light from the moon’s surface.
The Cassini probe found evidence of global distribution of the water signal.
And most recently, the Deep Impact spacecraft found evidence by infrared detection.
“The Deep Impact observations of the Moon not only unequivocally confirm the presence of [water/hydroxyl] on the lunar surface, but also reveal that the entire lunar surface is hydrated during at least some portion of the lunar day,” the authors wrote in their study.The amount of water on the moon is minuscule by Earth standards, with one ton of lunar surface holding about 32 ounces.
The findings of all three spacecraft “provide unambiguous evidence for the presence of hydroxyl or water,” said Paul Lucey of the University of Hawaii in an opinion essay accompanying the three studies. Lucey was not involved in any of the missions.
The new data “prompt a critical reexamination of the notion that the moon is dry. It is not,” Lucey wrote.
It makes sense though, doesn't it? In all the millions of years, the moon was bound to be hit by lots and lots of comets, comets made of ice. That ice was driven deep into the moons surface, where it was protected.