Trim fat from roast. Cut roast, if necessary, to fit in a 3 1/2 -4 quart crockery/ slow cooker. Mix water, vinegar, Worcestershire sauce and chili powder; pour over roast. Cover and cook on low-heat setting for 10-12 hours, or on high-heat setting for 5-6 hours. Remove meat from cooker, discard cooking liquid. Using two forks, pull the meat apart and return it to the cooker. Stir in BBQ sauce. Stir to coat meat. Cover, and cook on high-heat setting for 30-45 minutes, or till heated. Serve meat mixture in Kaiser rolls or hamburger buns with onion and pickles, if desired.