We don't insulate or anything else with our rainbutt, Derek. It just sits there and freezes without any harm and it is over 20 years old.

The only precaution we take now after last winter is to remove the top layer of ice back to clear water if the temperatures are set to freeze as low as they did last year. Last time the unfrozen water below the ice cap froze and because it had nowhere to expand the pressure split every water butt we possess. First time that has happened in 16 years of water collecting.

We have a half barrel fountain thingy with a pump in it in the garden. We just leave it out all winter but I make sure I empty the water down to half full (or half empty!) so that when the water expands when frozen, it doesn't split the barrel.

Useful question...
My waterbutts are very near to my house so I think that means they don't get quite so cold as other parts of the garden ..

Added to GoYpedia Waterbutts and barrels :o)

Remember to get some spare washers, and change the one behind the tap every six months.
Save every litre of water that comes your way.
We will need it, next summer.
Also keep the top covered, as birds think its there for them to drink, and drown. Horrible job, fishing them out.

Also depends on what kind of water butt you have - the plastic ones may well split, but my own wooden barrels with the metal rings have frequently frozen solid but never split.