The objective is to examine the influence of pore water on dynamic rupture processes in the context of deep geothermal reservoirs. We conducted stick slip experiments on thermally-treated, saw-cut westerly granite samples under triaxial . The samples were widely instrumented to allow measuring dynamic shear stress drops, temperature increases and acoustic emissions. Preliminary results showed that at a given effective confining pressure (Pc-pf), the dynamic shear stress drops were about 20 to 30% higher and slip distances were about 30 to 40% longer in dry samples than in water saturated samples. Following the same tendency, higher temperature elevations were recorded during nominally dry experiments. These results highlight the importance of pore water pressure in controlling dynamic frictional weakening, and suggest that water might inhibit dynamic weakening and so, rupture propagation in granitic rocks.