We already have a heated bucket with nipples, but I thought this idea had merit for those using the trough style waterer.
http://www.the-chicken-chick.com/2011/11/make-cookie-tin-waterer-heater-under-10.html
http://www.the-chicken-chick.com/2011/11/make-cookie-tin-waterer-heater-under-10.html