Cook potatoes in boiling salted water until tender. Drain, peel, and while hot, cut into 1/8 inch slices; sprinkle with the salt, pepper, mustard, sugar and flour. Heat water and vinegar to boiling point. Place bacon, sliced and chopped fine in skillet, fry light brown; add onions, brown slightly; add potatoes and the hot vinegar; heat through to absorb the vinegar and water; serve warm.