Melt butter in a microwave-safe baking dish on HIGH for 40 seconds. Stir in thinly sliced celery and thinly sliced onion. Cover with plastic wrap and cook on HIGH for 2 minutes, or until the onion is tender. Stir in tomato soup (undiluted), water, lemon juice, chopped parsley, sugar, and pepper. Cover and cook on HIGH for 5 minutes, stirring once. Spoon into serving bowls.