|MadSci Network: Earth Sciences|
Groundwater can be an important factor in faulting and earthmovements such as for earthquakes caused by faulting. I'm not sure, but doubt that water is necessary for plate tectonics to take place. This activity is on a continental scale and very deep seated. At great depths and very high temperatures molten rock may become a more important lubricant than water. At those depths water probably doesn't exist in the liquid form. I suggest that you pursue a more in depth answer by searching sites on the internet.
Try the links in the MadSci Library for more information on Earth Sciences.