Place the water in a saucepan over medium heat. Add the drained corn, celery, onion and parsley. Bring the water to a boil, then cover and simmer for 20 minutes.
Strain the vegetables and set them aside.
Return the corn stock to the saucepan over medium heat.
Add the warmed milk to the corn stock.
In a small bowl, combine the melted butter and flour to form a runny paste.
Whisk this into the corn stock until it is fully dissolved.
Add the salt and pepper, then heat to boiling.
Boil 2-3 minutes over medium heat.
Add the vegetables back to the broth and heat through.