Depends who you "believe" doesn't it? Christiansen's TES instrument, which is shown to have many flaws, or the Mars Odyssey neutron spectrometer that says there is vast reserves of water close to the surface. In my opinion, Christiansen is just veying for some attention with his low res "unable to see through dust" TES instrument.

http://planetary.org/html/news/articlearchive/headlines/2002/wet_mars.html

More Water Found on Mars

"December 11, 2002: Water, that elixir of life, has always been a holy grail of Mars research. With two spacecraft currently orbiting the planet, the Mars Global Surveyor and the Mars Odyssey, scientists now have an unprecedented amount of data to analyze in their water quest. The results of this treasure-trove of information are now showing, as several groups of researchers, relying on different sets of data, point to the presence of large amounts of water close to the surface of the Red Planet."