Many astronomers are convinced that early collisions between Earth and comets brought the vast amounts of water that now make up Earth's oceans. These oceans enabled life to get a foothold. On the flip side, the dinosaurs are certainly an example of how collisions between Earth and comets can also bring extinction to different lifeforms.
This would be an expedient method to get some water to the moon so the moon can be made inhabitable. Not a small project, still it would be more powerful than using rockets to carry water from the earth to the moon.