Preheat oven to 350 degrees F (175 degrees C). Grease one 2 1/2 quart casserole dish.
Blend together milk, cream cheese, onion dip and eggs.
In a saucepan over medium heat, combine water, margarine and salt. Bring to a boil and add instant potato mix; mix well. Add cream cheese mixture, mix well and pour into prepared dish.
Dot the top with margarine and bake at 350 degrees F (175 degrees C) for 30 to 45 minutes.
