Coat slow cooker with vegetable oil spray. Add rice, butter and salt to prepared slow cooker, then stir in boiling water. Cover and cook until rice is tender, about 2 hours on high.
Fluff rice with fork and season with salt and pepper to taste. Drape towel over top of slow cooker, cover with lid, and let sit for 5 minutes before serving. (This dish does not hold well on warm setting.)