Preheat oven to 425 degrees F.
In a large baking dish (about 9 x 13), stir together uncooked pasta, marinara sauce, water, and meatballs. Cover tightly with aluminum foil and bake for 35 minutes.
Uncover; stir. At this point you should check the pasta to make sure that it is firm but just about finished cooking. If it’s still too hard, cover the dish and return to the oven until pasta is al dente. Then move on to the next step.
Sprinkle mozzarella over the top and bake uncovered for 5-10 more minutes (or until cheese is melted and pasta is tender).