Heat the oven to 350°F and grease a 9-by-13-inch baking dish.
Mix the beef, rice, milk, egg, onion, salt and pepper gently until evenly combined.
Shape the mixture into 18 equal meatballs and arrange them in a single layer in the dish.
Whisk the tomato soup, water and Worcestershire until smooth and pour the sauce over the meatballs.
Cover tightly with foil and bake for 50 minutes.
Uncover and bake for 10 to 15 minutes more, until the rice is tender, the sauce has thickened and the meatball centers reach 160°F.
Rest for 5 minutes before spooning the tomato sauce over each serving.