In a skillet, cook bacon until crisp. remove to paper towel to drain; crumble and set aside. In bacon drippings, saute the onion until tender. Remove from the heat. combine flour, sugar, salt, celery seed and pepper; stir into onion mixture. Add water and vinegar. Return to heat; cook, stirring constantly, until mixture comes to a boil. Boil for 1 minute. Place potatoes and bacon in a large bowl; pour sauce over and toss gently. Serve warm.