Preheat oven to 350°. Prepare dough, and divide in half. Roll each half into a 9- to 10-inch round. Transfer rounds to parchment paper-lined baking sheets. Whisk together egg white and water just until foamy. Stir together pumpkin seeds, sunflower kernels, sesame seeds, and black sesame seeds. Brush rounds with egg white mixture, and sprinkle with seed mixture. Cut each round into wedges of random sizes, using a fluted pastry wheel. Separate wedges about 1 inch apart. Bake 16 to 18 minutes; cool on baking sheets on wire racks 30 minutes.