Preheat the oven to 350 degrees F (175 degrees C).

Combine ground beef, 1/2 cup condensed tomato soup, onion soup mix, bread crumbs, and egg in a large bowl. Shape into an 8x4-inch loaf; place on a large, rimmed baking sheet.

Bake in the preheated oven until meatloaf is no longer pink in the center and an instant-read thermometer inserted into the center reads 160 degrees (70 degrees C), about 1 hour 15 minutes.

Combine 2 tablespoons baking sheet drippings, remaining tomato soup, and water in a saucepan over medium heat; heat until mixture is hot and bubbling. Slice meatloaf; serve with sauce.