In a skillet, cook bacon until crisp; drain, reserving 2 tablespoons of drippings. Crumble the bacon and set aside. Saute the onion in drippings until tender. Stir in flour until thoroughly combined. Add water, vinegar,and sugar.Cook and stir until thickened and bubbly; Cook and stir 2 minutes more. Gently stir in beans and heat through. Sprinkle with bacon.