Taco Soup

1 medium onion, chopped
1 lb. 95% fat-free ground beef
15 oz. can stewed tomatoes
15 oz. can Mexican style diced tomatoes
8 oz. can tomato sauce
1 pkg. dry taco seasoning
1 pkg. dry ranch-dressing mix
15 oz. can red kidney beans, drained
15 oz. can pinto beans, drained
15 oz. can black beans drained
15 oz. can white corn (undrained)
1 cup water

Sauté chopped onions in nonstick skillet sprayed with nonstick spray. Add ground beef, brown and then drain grease. Add tomatoes, tomato sauce, taco seasoning and ranch dressing; stir well. Add beans and corn. Add water until desired consistency. Simmer over low heat for 30 minutes. Serve.