Potato and Mushroom Chowder

1/2 cup chopped onion
1/4 cup butter or margarine
2 tablespoons all-purpose flour
1 teaspoon salt
1/2 teaspoon pepper
3 cups water
1 pound fresh mushrooms, sliced
1 cup chopped celery
1 cup diced peeled potatoes
1/2 cup chopped carrots
1 cup light cream
1/4 cup grated Parmesan cheese

In a large soup pot, saute onion in butter until tender. Add flour, salt and pepper; stir to make a smooth paste. Gradually add water, stirring constantly. Bring to a boil; cook and stir for 1 minute. Add the mushrooms, celery, potatoes and carrots. Reduce heat; cover and simmer for 30 minutes or until vegetables are tender. Add cream and Parmesan cheese; heat through.