This may explain where some of the water on the Moon came from. I also find it really interesting that it took this long to discover this ice.
There are a couple of interesting notes here.
One is that water is downright plentiful in the solar system. Admittedly mostly as ice, and mostly in the outer solar system.
The Earth's own oceans are believed to be substantially the result of icy bodies impacting the Earth. Similar bodies would certainly have impacted the moon (I think the hit ratio is something like 1/20).
The reason we spent so long not even considering water on the moon, besides the fact that the regolith we found was dry, is the result of the very low pressure (meaning there's an extremely low sublimation temperature for water), and exposure to the sun.
It's important to note, that we determined water likely before we really found it. In essence, it was the process of determining that water could survive (in perpetual shadow for example) that made us really look.
(I'll stop crowding this thread for a bit now. Can you tell it's another passion of mine?)