Bring the water to a boil in a large saucepan. Add the beef shank, barley, carrot, turnip, leek and celery. Season with thyme, salt and pepper. Bring to a boil, then simmer gently over medium heat for 2 hours.
Remove the shank from the saucepan and cut the meat into small pieces. Return the meat to the saucepan and discard the bone. Return to a boil and then stir in the parsley. Serve very hot.