Insulate exposed pipes — especially those in unheated areas of your home, like the attic, crawl space, or garage. In moderately cold climates, inexpensive foam pipe insulation should do the trick. But if you live where winter is serious business, opt for thermostatically controlled heat tape (available at plumbing-supply stores). It doesn’t come cheap, but patching up water damage will cost you a whole lot more.
Open your cabinet doors. Kitchen and bathroom pipes can freeze in a hurry if, as is often the case, they abut exterior walls. By opening up the cabinet doors under your sink and bathroom vanity, you’ll keep those danger zones warmer.
Keep your faucets open. Contrary to what you may have heard, letting faucets drip is not a slam-dunk solution (in really frigid weather, even a roaring river will freeze). But it is true that letting the water flow very lightly will relieve the pressure inside the pipes and may prevent them from freezing — but if you live in a place with Arctic-like weather, all bets are off.
Leave the heat up. Don’t try to pinch pennies by lowering the temperature when you go out or (worse) turning off the heat in unused rooms. In cold weather, turning the thermostat down much below the upper 50s can be a recipe for disaster. And if you know that an unused room or closet has water pipes traveling through it, go one step further, and leave the door open so that heat can circulate from the rest of the house.
Turn the water off. Whenever you leave home for more than a day — or even overnight during a wicked cold snap — shut off the water at the main valve. Then turn on all of your faucets, and let them flow until they stop. Even if any water remaining in the pipes freezes, it won’t expand enough to cause a rupture.