But it looks like it might not have been as much as originally thought. Pretty cool though, especially when we get people to Mars and try and mine the ice for our own needs.
http://www.cnn.com/2002/TECH/space/12/08/mars.odyssey.ap/index.html
http://www.cnn.com/2002/TECH/space/12/08/mars.odyssey.ap/index.html