In a large stock pot, combine chicken stock, water, vegetable soup base, dried thyme, poultry seasoning, and dried parsley. Simmer 15 minutes while you chop veggies and chicken.
After 15 minutes, add chopped onion, chopped celery, sliced carrots, and barley. Start to simmer, and when the barley is nearly done (about 45 minutes) add the diced chicken. You may want to add a cup or so of water if the soup reduces too much.
When the barley is done to your liking, season the soup with fresh ground black pepper and salt to taste, and serve hot. (Be sure to taste before adding salt if using canned chicken stock, which can be rather salty.)