Put a small wire rack or a silicone rack (if you don't have a rack you can use aluminum foil to form a ring or use a sliced onion) in the bottom of the slow cooker.
Mix together the softened butter, rosemary, garlic powder, paprika, onion powder, sea salt, and pepper.
Pat the turkey dry. Carefully lift the skin enough to rub ½ of the butter mixture on the turkey underneath the skin. Rub the remaining butter mixture over the skin.
Place the turkey breast on the rack. Pour the water into the slow cooker.
Cover and cook on low for 5-6 hours or until the turkey reaches an internal temperature of 165˚F.
Transfer the turkey breast to a rimmed baking sheet and brown the skin under the broiler for 3-4 minutes until golden, watching carefully so that it doesn't burn.
Video
Notes
Storage: Allow the leftovers to cool and then store them in an airtight container in the fridge for 3-4 days.