Place the pork roast on a flat surface and pat dry with paper towels. Generously rub about 1/4 cup of the pork dry rub onto the roast and transfer to the dish of a 6-quart slow cooker. Add the water, cover with lid, and set to cook for 6 hours on high or 10 hours on low. Cooking time will vary depending on the size of your roast.
Half an hour before serving, remove the pork roast from the slow cooker onto a large cutting board and shred the meat between 2 forks. Place the meat back into the slow cooker and stir to combine with the cooking liquid. Cover and cook on low for an additional 30 minutes.