Combine the hamburger, cracker crumbs, egg, chopped onion and raw rice.
Form the mixture into 1-inch meatballs.
Heat the tomato soup and 1 can water in a heavy pan.
Bring to a boil.
Add the meatballs one at a time.
Turn the meatballs once.
Reduce the heat and simmer for 1 hour, or until the rice is tender.
Stir occasionally to prevent sticking.
Serve the thickened tomato soup over mashed potatoes, if desired.