Preheat the oven to 350 degrees F (175 degrees C).
In a shallow three-quart baking dish, toss uncooked macaroni and melted butter together, to coat the macaroni and the inside of the dish. Add cheese, and stir lightly to distribute. In a medium bowl, whisk together the evaporated milk, water, eggs, mustard powder, salt, white pepper and cayenne pepper. Pour into the baking dish with the macaroni.
Bake uncovered for 45 minutes, or until the center is set. Remove from the oven, and let stand for 5 minutes before serving.