Remove and discard chicken skin. Rinse chicken; drain and pat dry. In a Dutch oven, combine chicken, broth, onions, celery, carrots, poultry seasoning, garlic powder, the 1/2 teaspoon salt and pepper. Bring to a boil. Lower the heat and simmer, covered, about 30 minutes or until chicken is cooked through. In a small bowl, whisk together the cold water and the 2 tablespoons flour. Stir into chicken mixture. Cook, stirring constantly, until mixture starts to thicken, about 2 to 5 minutes.