1. Combine raisins and rum. Cover and set aside.
2. Combine evaporated milk and 1 1/2 cups water in a medium saucepan. Bring to a simmer over medium heat. Add sugar, stirring to dissolve. Remove from heat.
3. Pour milk mixture into a 3-quart electric slow cooker. Stir in rice and salt. Cover and cook on LOW for 4 hours or just until pudding is set in center, stirring after 1 hour and again after 3 hours.
4. Stir in raisin mixture and nutmeg; let stand, uncovered, 10 minutes. Serve warm.