You can take it off the chain and set it on the heated metal base.
Alternatively, you could use a heated dog bowl or those heated plastic waterers for chickens.
I just use the black fortex rubber tubs, and go out there a couple times a day, step on them when they are upside down and pour more warm water in. No electricity needed. But we don't get much freezing weather so I don't have to do this all winter.