Dice (and peel if desired) potatoes. Combine with onion in slow cooker and cover with water. Cover and cook on low for 5 to 6 hours or high for 2 to 3 hours. Remove from cooker, drain and return to slow cooker.
Cook bacon in a skillet over medium heat. Stir in flour, sugar, mustard, salt and pepper. Mix well. Add vinegar and water. Cook for several minutes or until thickened. Pour over potatoes and onions. Turn control to high. Cover and cook for 30 to 40 minutes or until mixture is hot.