Pipes may be insulated to prevent freezing, but this is not a
completely dependable method. Insulation does not stop the loss of heat
from the pipe--merely slows it down--and the water may freeze if it
stands in the pipe long enough at below-freezing temperature. Also, if
the insulation becomes wet, it may lose its effectiveness.
Electric heating cable can be used to prevent pipes from freezing. The
cable should be wrapped around the pipe and covered with insulation.