Place water and bouillon in a medium pot. Bring to a boil. Add broccoli and onion and cook for 10 to 12 minutes.
Meanwhile, combine margarine, flour, milk, and cream cheese in a large pot. Cook until thick, stirring constantly. Add cheddar cheese and stir until melted. Pour cooked broccoli and onion, including the water, into cheese mixture. Stir well. If you desire a thicker soup, add 1/2 cup milk with 1 T cornstarch to soup.