The temperature alert threshold for pipes to burst is 20 degrees.  Anything above this scientist have found that exposed pipes will not burst but once the temperature drops to 19 degrees pipes begin to fail.  The reason you don't hear about protecting pipes in the northern United States is because their pipes are built within the house.  Many pipes in the southern U.S. are on the exterior of the home.  Where we live is more likely to have unprotected pipes because we rarely have temperatures in the 20s. 

When there is a wind chill,  the wind chill will accelerate the ice blockage.

*** A note about pools when the temperatures get into the lower 20s.***  I spoke with a pool expert and he told me let the pools pump run.  The pool won’t freeze and letting it run will keep above freezing water flowing through the pipes.

If you are concerned about your pipes bursting in what may be below-20 degree temperatures, check out the Insurance Institute for Business and Home Safety.  It's an excellent source of information.