The Solar Wind Theory illustrated

Schematic shows daylight cycle of hydration, loss and re-hydration on the lunar surface, as indicated by calibration images collected by EPOXI during as close as 8 million km encounters with the Moon in 2007 and again, on two separate days in June 2008. In the morning, when the moon is cold, it contains water and hydroxyl molecules. The Solar Wind Theory holds the water and hydroxyl are, in part, formed from hydrogen ions in Solar Wind. By local noon, when the moon is at its hotest, some water and hydroxyl are lost. By evening, the surface has cooled again, and is returning to a state equal to that seen in morning.

Regardless of location or terrain type the entire surface of the moon is hydrated during some part of the lunar day. [University of Maryland/McREL. ]