Groundwater Expo (Nov 29 - Dec 2) in Las Vegas. But I'm partial to their groundwater summits where a lot more focused information regarding groundwater happens.
The 2012 event is more precisely called: "2012 NGWA Ground Water Summit - Innovate and Integrate: Succeeding as a Groundwater Professional in a Water-Short World."
May 6-10, 2012 in Garden Grove, CA at the Hyatt Regency Orange County will be this years venue, and the program looks jam packed. All the way from the keynote speaker (Pat Mulroy, Las Vegas Valley Water District, Southern Nevada Water Authority) to the 30 already accepted session proposals, this looks like an interesting and well rounded event. Use the link above to see all the session details.
As the event gets closer, I'll do another post on it - as I'm sure will others in the water community. BTW, you should note that the submission deadline for abstracts is still a few days away (11:59 P.M. November 30, 2011) so if you are inclined, submit away.
While the looming abstract submission deadline is the main reason I'm so early with this announcement, the other reason is a burning desire to finally get something water-related announced before @WaterWired does! There you have it. (Just kidding Michael. I'm certain you will do the subject a thorough and much more professional rendering when the more appropriate time comes - and I'll look forward to it! You are not only an institution, but an inspiration as well!) More later.