I have found slight slurry finishes better. BUT I do have a few hard suitas and asagis even that finish water only very nicely. As was said, look at the bevel and see how polished or scratchy it is after slurry, or water. If you see polishing, then there is further refinement, if not then the edge is degrading. Some stones scratch water only, and HHT is reduced sometimes after water only depending on the stone. Hone and shave trying different things will get you where you want to be. Heavy resistance and suction sometimes causes stone particles to be sucked up out of the stone and wreck the bevel. You can have the best of both if you rinse the stone but leave some residual slurry on the blade.