In a mixing bowl, combine the cream of mushroom soup, water, chopped onion, uncooked macaroni, cubed cheddar cheese, and margarine.

Pour the mixture into a greased 8 x 8-inch baking dish, cover, and refrigerate overnight.

When ready to bake, preheat your oven to 350°F (175°C).

In a small bowl, mix together the fine bread crumbs and melted margarine.

Sprinkle the bread crumb mixture over the top of the macaroni mixture in the baking dish.

Bake the macaroni bake in the preheated oven, uncovered, for one hour or until golden and bubbly.

Serve hot and enjoy this comforting and creamy macaroni bake!