In a large pot, cook the ground beef and onion over medium heat until the beef is browned and the onion is tender.
Add the garlic and cook for another minute, stirring constantly.
Stir in the spaghetti sauce and water and bring to a boil.
Add the spaghetti noodles and reduce heat to a simmer.
Cover and cook for about 15 minutes, stirring occasionally, until noodles are tender.
Season with salt and pepper to taste.
Serve with a sprinkle of Parmesan cheese if desired.