When a long spell of cold weather or freezing temperatures are expected it's a good idea to protect a water butt against the winter cold. When the temperatures drop the water inside the water butt expands as it freezes. The result is shown in the image left, the severe weather can split the plastic and the entire water-butt will fracture.
The photo shows the full extent of the problem which happened during a sustained cold period. Caught out by the sudden very cold weather the complete water-butt froze and fractured. An expensive oversight. To avoid this problem, before the bad weather strikes disconnect and drain the water butt, and leave it disconnected until the worst weather has passed. To freeze a large solid a mass of water requires a spell of sub-zero temperatures, which can be experienced in December & January with temperatures remaining below freezing for many days. Simply re connect the water butt in the early spring.