Sauté onion in butter. Add 1 cup water, celery, and potatoes.Cover and cook until nearly done. Season with salt and pepper.
When vegetables are tender, add milk.
Bring to a boil. Remove from heat.
Add water to oysters and heat. Remove any scum.
When edges curl, combine with milk and vegetables.
Let stand few minutes for flavors to blend.
Serve hot. Serves 6.