When you have frozen water pipes you call a plumber to come out to help thaw the frozen water pipes.
Also if you have broken water pipes the plumber will need to replace the broken water pipes which can get costly.
In extremely cold temperatures it may be hard and even impossible for a plumber to get the water pipes to thaw and sometimes you'll need to wait for a warmer day.
During extreme cold you should make sure to keep water available for drinking, bathing etc so gather water up before it gets too cold and possibly freezes the pipes.
Also having a frost free water hydrant in your yard is a good idea too so that you can still have water if your other water pipes freeze up.
Frozen water pipes can thaw themselves out if the water pipes are warm enough to thaw.
You can also pour cold water over the water pipes to help thaw them out but make sure to leave a faucet open so the water can flow through and reduce the pressure on the water pipes.
If your water pipes are under the house you can place a heater safely under the house and allow the water pipes to get some heat.
Or if you have a basement make sure to try and keep the basement above freezing which prevents frozen pipes and any exposed pipes outside should be insulated and protected from the wind and cold.
The reason water pipes tend to burst in winter is because of the ice molecules expanding.
As that ice expands it pushes against the pipe which then causes the pipe to burst or crack open.
Basically the way frozen water pipes burst is when water freezes inside pipes, the water molecules expand.
The ice in the water pipes then expands and pushes the water toward the faucet, causing a significant amount of pressure buildup between the ice blockage inside the pipe and the faucet which then leads to the water pipes bursting.
Frozen water pipes don't always burst.
However most water pipes do eventually burst and it also depends on the material the water pipes are made from.
Copper Pipes, PVC, CPVC pipes etc all tend to crack or burst when frozen.
The pex pipe does not burst when frozen though as it can stretch.
To prevent frozen water pipes make sure to leave a water faucet or water faucets dripping and running at a slow stream of water flow.
The water flowing through the pipes reduces the water pressure on the pipes and prevents the pipes from freezing up.
This helps to prevent frozen pipes and also prevents burst water pipes.
Also insulate any exposed water pipes and use some heat tape for water pipes to keep them from getting too cold and freezing.
Water pipes freeze when they get as cold as 32 F or below and if the wind is blowing the water pipes can freeze faster.
To thaw and fix frozen water pipes you call a plumber.