Heat the oven to 325 degrees. Lay the pork on a cutting board and sprinkle all sides liberally with salt. Nestle the meat into a baking dish and drizzle the water or orange juice on and around it. If using the optional flavorings, nestle the garlic and bay leaves around the meat, then sprinkle with oregano and black pepper. Cover tightly with foil and slide into the hot oven. Set the timer for 1 ½ hours.
Remove the pan from the oven and uncover. Test the pork: it should be almost tender when pierced with a fork. Raise the oven temperature to 450 degrees. Slide the uncovered pan back in the oven and roast until all the liquid has evaporated and only the rendered fat remains, about 30 minutes. Use a large metal spatula to turn the meat over, break it into large chunks, return to the hot oven and roast for another 20 minutes or so, turning the meat every 7 or 8 minutes, until the carnitas are richly golden all over.
Arrange the carnitas on a warm serving platter and sprinkle with salt. Serve with the guacamole, salsa, limes and warm tortillas.