In a large saucepan, bring the water to a boil. Add the broccoli and onion; boil for 10 to 12 minutes. Add the cheese, salt, pepper, and garlic powder. Cook over medium heat, stirring constantly, until the cheese melts. Add the milk, cream, and butter. Heat to boiling, stirring constantly.

Add the water to the flour and mix until smooth. Add slowly to the hot soup, stirring rapidly. Continue to cook, stirring constantly, until the soup is the consistency of heavy cream. Serve hot.