Nice graphic on here depicting how the water table can now be shown:

http://earthobservatory.nasa.gov/New...3?img_id=17534

"Using an advanced mathematical technique known as data assimilation,
hydrologists are now combining GRACE data with numerical land surface
models in order to produce the best possible maps of terrestrial water
storage. The results (right column) combine the accuracy of GRACE data
with the finer detail and more frequent updates of the models.
Furthermore, while GRACE can only provide information on the total
water stored in the whole basin, the assimilated model output
separates terrestrial water storage into its primary components:
groundwater, soil moisture, and snow."