Preheat the oven to 350 degrees F (175 degrees C).
Bring water and 1/2 cup butter to boil in a medium saucepan. Remove from the heat and stir in stuffing mix. Cover and let stand for 5 minutes. Fluff with a fork.
At the same time, cook sausage in a large, deep skillet over medium-high heat until browned and crumbly, 5 to 7 minutes; drain.
Transfer stuffing mix and sausage to a large bowl; mix in celery, onion, melted butter, and poultry seasoning. Slowly stir in desired amount of chicken broth. Transfer to a medium baking dish.
Bake, covered, in the preheated oven until lightly browned, about 30 minutes.