Preheat the oven to 400° and line a baking sheet with foil. In a large bowl, mix the salt with 3 tablespoons of water until it resembles wet sand. Spread half of the salt in the center of the baking sheet and top with half of the thyme, rosemary and parsley sprigs. Set the pork loin on top of the herbs. Spread the remaining herb sprigs over the pork and cover completely with the remaining salt, packing it all around the loin. Roast the pork for about 35 minutes, until an instant-read thermometer inserted in the thickest part of the meat registers 125°. Let stand for 5 minutes.