Preheat the oven to 400 degrees F (200 degrees C).
Rinse pork; pat dry with paper towels. Rub butter all over the skin. Sprinkle salt over the skin.
Place pork leg on a rack in a roasting pan. Pour water into the bottom of the pan. Cover pan securely with aluminum foil so that steam will not escape.
Roast in the preheated oven for 30 minutes. Remove foil. Reduce heat to 320 degrees F (160 degrees C).
Continue baking, basting with drippings every 30 minutes, until skin is crisp, about 3 1/2 hours. An instant-read thermometer inserted into the center should read 176 degrees F (80 degrees C).
Place pork leg on a serving platter. Slice into bite-sized portions.
