If you've ever had the misfortune of having a water pipe freeze and burst, you know that's an experience you only want to have once in a lifetime. It's not just the aggravation and cost of fixing the pipe itself, it’s the damage the burst pipe does to the rest of your home. Walls, ceilings, floors and personal possessions stored in the basement or crawl space can all be ruined. Damages are sometimes covered by insurance, but depending on circumstances, you might just be on your own. Plus, even if your home insurance does cover the damage, you're still going to be living in a construction zone until the mess gets repaired. Obviously, making sure your pipes don't freeze is a much better option.
Draining the Lines
Before cold weather, shut off the valves supplying your outside water lines. Individual supply lines running to the outside (hose bibs for example) will usually have a shut off valve on the inside of your home, close to where the supply goes outside. Drain the outside lines by opening the tap and then leave it the open position. This will allow any small amount of water that might be left in the line to freeze and expand without causing any damage.
The major damage from frozen pipes comes when a home is unoccupied during a cold spell and the pipes freeze solid. When the pipes warm up, water flows out of the broken pipes into the walls and down through ceilings creating thousands of dollars of damage. If you're going to be away from your home for a while, you can prevent this from happening by actually shutting off the water supply to your entire home, then opening the taps and draining the water in the pipes. (Be sure you shut off your hot water tank as well.) This way, even if your furnace does stop working while you're away, there isn’t any water in the pipes to freeze.
Insulating Your Pipes
Check any water pipes that run close to outside walls as well as pipes in unheated crawl spaces or garages where they will get cold. On the pipes inside your home, put some fiberglass insulation between the pipes and the walls to help keep them warm and prevent freezing.
Pipes running through unheated spaces should be covered with insulation. Preformed pipe sleeve insulation shaped to go right around a copper water pipe is an inexpensive option. Butt the pieces together and tape them in place.
Heating the Pipes
A better but slightly more expensive solution is to wrap the pipes with electrical heating tape. These tapes are specifically designed to wrap around water pipes and act like a little electric blanket preventing the pipes from freezing. Be sure any heating tapes you buy have been approved by Underwriters Laboratories and have the UL symbol on them.
Keep in mind that a hot water pipe running through an unheated area can freeze just as solidly as a cold water pipe, so you need to insulate both hot and cold water pipes.
Running the Taps
If you get caught by a sudden cold snap or haven't had a chance to insulate your pipes, a short-term solution can be to leave a tap running slowly to prevent them from freezing. It's wasting water and will definitely add to your water bill, but as a quick fix it's a better option than having a pipe freeze and crack.
Repairing the Damage
Even with your precautions, if a water pipe freezes while you are home, it's a manageable problem.
The first thing is to determine if the frozen pipe has actually burst or is just frozen and blocking the water flow. If the pipe has burst, you'll need to repair the pipe before you thaw it. (See "The Basics of Working with Copper Pipe" and "How to Cut and Join Copper Pipe.")
For a pipe that has frozen but not burst, the first thing to do is shut off the water flow to the pipe. Depending on how your home is "plumbed" you may need to shut off the main water supply to the entire house. The main shut off valve for your house is usually close to your water meter or where the water supply comes into your home. Now open a couple of faucets so any steam or water can escape while you thaw the pipe.
You want to heat the frozen pipe slowly, being sure the water inside doesn't boil or the pipe become too hot to touch, so don't use propane or welding torch to melt the ice. Instead, use a hairdryer, a small space heater aimed at the blockage or wrap the frozen section with pipe heating tape and plug it in for a while. Alternatively, you could just wrap the frozen pipe section with warm cloths and keep wetting them with hot water (from the kettle) until the ice melts.