Cut chicken into 1-inch pieces. In a 3-1/2- or 4-quart slow cooker combine the chicken pieces and onion. In a medium bowl stir together the soup and water. Pour over chicken and onion.

Cover and cook on low-heat setting for 6 to 7 hours or on high-heat setting for 3 to 3-1/2 hours.

Cook noodles according to package directions. Drain. Just before serving, stir sour cream into mixture in cooker. To serve, spoon stroganoff mixture over hot cooked noodles. If desired, sprinkle with black pepper. Makes 6 to 8 servings.