In the skillet, heat ¼ cup of the olive oil until it shimmers. Add the garlic, sage, and rosemary and cook over moderately high heat, stirring, until fragrant and the garlic is just beginning to brown, about 1 minute. Turn off the heat. Add the beans and toss to coat.
Transfer the cannellini beans and oil mixture to the food processor. Add the water, season with salt and cayenne and process to a fairly smooth puree, about 2 or 3 minutes. Serve in a small bowl with the remaining olive oil drizzled on top.
PITA CHIPS: To make plain pita chips, cut a round of pita into 4 to 8 slices and toast for 2 or 3 minutes in a toaster oven or on a baking sheet in the oven at 350° F. To make the herbed pita chips, make extra herbed olive oil mixture and brush it on top of the pita round. Cut into slices and toast as above.