1. Place the water into a large soup pot over medium high heat.
2. Add the potatoes, celery and onion.
3. Boil vegetables until as tender as you desire.
4. Add the butter, salt and pepper.
5. Pour in the milk and stir well.
6. Bring back to a boil.
7. Cook until liquid is thick and creamy.
8. Sprinkle with the parsley just before serving.