Place the pork shoulder, water, orange juice, milk, salt, and pepper in a large pot or Dutch oven.
Bring to a boil over medium-high heat, then reduce heat to low, cover, and simmer for 2 to 3 hours, or until the pork is very tender.
Remove the pork from the pot and shred it using two forks. Discard any excess fat.
Heat the vegetable oil in a large skillet over medium-high heat. Add the shredded pork and cook for 5-7 minutes, stirring occasionally, until it's browned and slightly crispy.
Serve hot, typically with tortillas, onions, cilantro, and salsa.
Notes
For extra crispy carnitas, you can broil the shredded pork for a few minutes after browning in the skillet.