1. To prepare the lamb, place the leg of lamb in a large mixing bowl with 1 cup water, the vinegar and salt.
2. Marinate, covered, in the refrigerator for 4 to 6 hours, turning occasionally.
3. Remove the lamb from the marinade and transfer to the grill. Grill over indirect medium-high heat for about 2 hours, basting every 15 to 20 minutes with the sauce. (The internal temperature of the leg of lamb should reach 135°F for medium-rare.)
4. Let the lamb rest for 15 minutes before carving.