In 3 1/2- to 4-quart slow cooker, layer onion, garlic and beef. Pour soup and water over beef.
Cover; cook on Low heat setting 5 to 7 hours.
Stir noodles into mixture. Increase heat setting to High. Cover; cook 20 to 30 minutes or until noodles are tender. Stir in sour cream. Garnish individual servings with parsley.