Preparation - In a large skillet, brown the ground beef and onion over medium heat; drain. Stir in the water, taco seasoning and tomato sauce. Bring to a boil, then reduce heat and simmer for 20 minutes. Stir in the cooked macaroni, salsa, and 1-1/2 cups shredded cheddar. Pour into a greased 2 quart baking dish. Top with the remaining cheese. Bake in a preheated oven at 350º for 30 minutes.