1. Saute celery, onion, and mushrooms in butter until softened. Stir in chestnuts and cook another 1 or 2 minutes.
2. Combine the sauteed mixture with everything else except water, then slowly add water until bread is thoroughly saturated. Mix together with your hands for at least 2 minutes, squeezing to form a heavy, thick consistency. Stuffing should be pasty, not crumbly.
3. Refrigerate promptly and age at least 12 hours, tossing with a fork as often as possible before use.