In a small mixing bowl, combine the salt, paprika, cumin, oregano and chipotle powder and stir to evenly combine.
Cover the lamb roast with the dried mustard, then evenly distribute the spice mix all over the lamb. Make sure to get it into all of the crevices as best you can.
Place the lamb in the slow cooker, cover and, if time permits, place in the fridge to marinate overnight.
When you are ready to cook the lamb, pour the water into the slow cooker and turn the heat to high; cook for 6 hours.
When fully cooked, the lamb should shred easily with a fork. Remove all but one cup of the cooking liquid from the slow cooker and shred the lamb.
Use the rest of the cooking liquid to adjust seasoning as needed.