Sprinkle surface of roast with lemon juice, 1/2 teaspoon salt, oregano, and 1/4 teaspoon pepper. Place roast, fat side up, in a large roasting pan; insert meat thermometer, if desired.
Bake roast, uncovered, at 450° for 10 minutes. Pour water and wine over roast; reduce heat to 325°, and bake 1 hour and 35 minutes.
Sprinkle potatoes with remaining salt and pepper; arrange potatoes around roast, and bake an additional 1 hour and 20 minutes or until meat thermometer registers 170° and potatoes are tender. Let roast stand 10 minutes before carving.