Pour 1 ounce dry vermouth into each of 12 (2-inch) ice-cube molds (such as King Cube). Add 1 teaspoon fresh lemon juice and 1/4 cup water to each mold. Place 1 to 2 fresh basil leaves into each mold. Place molds in freezer; freeze 8 hours or until solid. Serve ice cubes in your favorite simple summer cocktails.