http://www.sciencemag.org/news/2019/04/moon-losing-200-tons-water-year-meteorite-strikes

When meteorites slam into the moon, they undoubtedly kick up a little dust. Now, a new study suggests they also shake loose quite a bit of water—something on the order of 200 tons each year.

Planetary scientists were tipped to the leaching after reviewing sensor data from a moon-orbiting probe. Between November 2013 and April 2014, the Lunar Atmosphere and Dust Environment Explorer recorded occasional spikes in the numbers of particles, including water molecules, that were lofted off the moon. Of the 39 spikes, 29 occurred within 48 hours of the moon and Earth passing through annual meteor showers that are broad enough to hit both bodies. In general, the stronger the meteor stream, the more particles were tossed into space from the moon, the researchers report today in Nature Geoscience.