Place meat and water in a large heavy saucepot.
Simmer, covered, until tender, about 3 hours.
Remove meat and reserve 1 cup of the beef broth.
Cool and shred meat; set aside. In the same saucepot in which the meat was cooked, melt butter.
Add onion; sauté until tender. Stir in sugar, salt, mustard, ketchup, vinegar, Worcestershire sauce and the reserved 1 cup beef broth.
Add shredded beef; mix gently.
Simmer, covered, for 30 minutes.