Cook the bacon in a large pan over medium heat, until crisp; drain on paper towels. Pour off all but 1 Tbsp. of the bacon grease. Add the leek and cook, stirring often, until tender.
Add the butter, stir to melt. Add the flour and 1 tsp. salt. Season with pepper and stir for 1 minute. Whisk in the milk, cream, and 2 cups water. Bring to a boil, reduce heat to medium, and simmer for about 5 minutes or until slightly thickened. Combine the three cheeses in a large bowl. Stir one cup of the cheese mixture into the sauce, along with the bacon and the parsley.
Place uncooked macaroni into an 8x8" caserole dish. Top with the sauce and stir to coat pasta. Sprinkle with the remaining 1/2 cup cheese. Bake in a preheated 350-degree oven for about 30 minutes or until sauce begins to bubble and pasta is tender. Let stand for 10 minutes before serving.