Mix first six ingredients. Place roast in a 5-qt. slow cooker; add water. Pour ketchup mixture over top. Add cookie crumbs. Cook, covered, on low until meat is tender, 6-8 hours., Remove roast from slow cooker; keep warm. Strain cooking juices; skim fat. Transfer 4 cups juices to a saucepan; bring to a boil. Mix cornstarch and water until smooth; stir into cooking juices. Return to a boil; cook and stir until thickened, 1-2 minutes. Serve with roast.