Heat oven to 350 F coat a 1 1/2 quart baking dish with cooking spray.
Microwave 2 tablespoons butter till melted and stir in paprika and breadcrumbs and set a side
Melt remaining butter in a sauce pan over medium heat add flour stirring constantly untill bubbly and lightly browned
Stir in milk, water, and salt and bring to a boil over medium heat stirring constantly. Stir in 2 1/2 cups shredded cheese and nacho cheese sauce and cooked macaroni and mix well.
Pour into prepared dish and top with 2 cups shredded cheese and breadcrumb mixture and bake for 25 to 30 minutes or till lightly brown.