i dont know of any heaters but we used to just bring the water buckets inside the garage at night, let them thaw, and put out fresh water in the mornings. the dogs would usually drinnk quite a bit in the morning, and then around noon or so i would occasionally see them break thru the thin layer of ice that had formed. Or on really cold days, just keep the buckets in the garage and offer fresh water twice a day. dogs did fine this way, they dont need as much water in cold weather. although this method is a little more labor intensive, your probably going out to feed them twice a day anyway.