If the water detected on the moon is found to be in error or proves to be to difficult to extract insufficient for our needs, there may be another source. Water, in the form of Ice, was detected on an asteroid. This new evidence can add insight into how the Earth came to have water. The theory that the water was brought to earth through celestial impact now has some supporting evidence.
http://spacefellowship.com/2009/10/08/more-water-out-there-ice-found-on-an-asteroid (via http://pajamasmedia.com/instapundit/86484)
"For the first time, astronomers have confirmed that an asteroid contains frozen water on its surface. Analysis of asteroid 24 Themis shows evidence of water ice along with organic compounds widespread across the surface. The scientists say these new findings support the theory that asteroids brought both water and organic compounds to the early Earth, helping lay the foundation for life on the planet."