We have a cold water storage tank in the loft, which is not properly
lagged at the moment. My neighbour is convinced there is risk of
flooding of the water freezes then thaws. The tank is made of plastic
(PVC?) not lead. The lid is loose, leaving plenty of space for
expansion. To my mind, freezing would be an inconvenience but no risk
to the integrity of the tank.

However, she also mentioned the inlet and outlet pipes. Could they
freeze and present a risk? Anyone venture an opinion?