Boil box of elbow macaroni according to the instructions on the box. Melt stick of butter in small saucepan. Do not let butter brown. Once butter is melted add can of evaporated milk to saucepan. Cook on low and stir frequently to prevent sticking to the pan. In a separate bowl, mix cold water and flour. Combine well. Add water and flour mixture to the saucepan of milk and butter. Stir in seasoning salt and black pepper. Season to taste.
Drain and rinse elbow macaroni and rinse with cool water. Spray bottom and sides of baking dish with cooking spray. Place a layer of elbow macaroni across bottom of baking dish. Cover with a layer of shredded sharp cheddar cheese. Cover with a ladle full of milk and butter mixture. Repeat. Cover top layer with slices of American cheese. Sprinkle top of American cheese with paprika.
Bake at 400 degrees F for 30-45 minutes or until top layer is fully melted.