1. Heat the oven to 350°F Beat the egg and water in a small bowl with a fork or whisk.
2. Unfold the pastry sheet on a lightly floured surface. Roll the pastry into a 16-inch square. Cut the pastry square into 8 (8 x 4-inch) rectangles. Cut the rectangles diagonally into 16 triangles. Arrange about 2 teaspoons chocolate chips down the center of each triangle. Starting at the wide end, roll each triangle up, bending the edges in to form a crescent. Place the pastries seam-side down on a baking sheet and brush with the egg mixture.
3. Bake the pastries for 20 minutes or until they're golden brown.