Boil potatoes until just tender. Drain, peel and slice into a large bowl. Set aside.

In a skillet, cook bacon until crisp. Drain bacon and discard all but 1/3 cup of drippings.

Sauté onions in drippings until tender, add flour, sugar, slat, celery seed, mustard and pepper. Gradually stir in water and vinegar and bring to a boil, stirring constantly.
Stir and cook for 2 more minutes.

Crumble bacon and stir into potatoes. Pour vinegar mixture over potatoes, stirring to coat. Sprinkle with chopped parsley.