On Thursaday, groundhogs the country over had their annual moment of glory (one wonders if they like all the attention, or would have preferred other professions). Per Wikipedia's tally, their weather predictions were split: Fourteen reputable groundhogs saw their shadows, forecasting six more weeks of winter, and 14 saw cloudy skies and therefore spring a-coming (Moscow's groundhog, Archi, apparently slept in).
So as to not be wildly disappointed (and, hopefully, pleasantly surprised), we're prepping for cold weather and snow. And not just emotionally—it's a good time to be sure the pipes in your house are ready for a drop in temperature.
As you know because of that one incident last summer with a beer in the icebox, water expands and pipes can burst. With potentially costly consequences. If your home isn't properly insulated—or if you live in a region that doesn't normally see freezing temperatures, like the South, where construction hasn't always accommodated for glacial weather—a drop below 20º F is worth prepping for.
Understanding how pipes freeze is the best way to be equipped: As temperatures drop, blockage (i.e., ice) can form along the inside length of a pipe, which pushes the unfrozen water towards the ends of said pipe with unwieldy pressure. (The best description I've read of this is that it acts "like a piston.") The result is often that pipes burst where they aren't frozen—downstream from that icy location.
So: By preventing that freezing in the first place (with thorough insulation), and also lessening pressure at the ends of a pipe, you can prevent the bust and resulting flooding. Here's how:
Seal up any cracks or holes in the walls. These can sometimes appear where the sill plate meets the foundation—go in the basement and look for any light coming through cracks at eye level, or feel around for any cold air creeping in, and patch them with expanding foam sealant or silicone caulk. Is there a hole left from that time you tried to get a cable through the wall? Patch it.
Insulate pipes in drafty areas. Think of the places in your home that aren't as well insulated as, say, the interior walls: Are there any pipes in the attic, basement, crawl space, or in the backs of cabinets that are more exposed to drafts or the elements? If yes, insulate them using fiberglass or foam coverings. Simply wrap lengths of it around the entire exposed section of any problem-zone pipes; they've got a handy slit in one side, like a hot dog bun, that seals shut once in place. Electric heating tape and cable are also available if the temperature is dropping wildly—if you're going to go that route, be sure to follow the product instructions precisely so there's no risk of fire.
Don't forget the elbows and T's! In addition to insulating the lengths of those pipes, you'll want to cover the corners (elbows) and three-pronged, T-shaped joints—a little bit more annoying to figure out with the foam casings, but necessary. You can either buy foam connectors that are designed to go over those joints (here and here) or cut your long pieces of foam to fit over them. This is a big one—don't leave any bits of problem-area pipe exposed!
Shut off and drain outdoor pipes: If some pipes are actually on the exterior of the house, it's better to cut off their water supply rather than try to insulate it: Shut off water to those pipes and leave any attached valves open so they can empty out and be free of pressure. That includes the opening (called a "hose bibb") where you screw in the garden hose.
On an extremely cold night, leave indoor faucets at a trickle.
Since these indoor pipes are better insulated, this is only necessary if it's getting bitingly chilly. Turn the faucet on just a tiny bit (a drip will do!) so that warm water is moving through it, keeping the contents of both hot and cold pipes in motion to prevent freezing.
Leave the thermostat be. Rather than turning the temperature up and down, keep it at or above 68º F at all hours. If you're going out of town for an extended amount of time, consider shutting off the water and draining all your pipes ("winterizing").
Leave cabinet doors with pipes inside them open. This will allow warm air to circulate through, and around the pipes.
But close the garage doors. You did this instinctively, right?
If you wake up to get a glass of water and there's none coming out of your sink's faucet, don't panic. Keep the faucet open and call your plumber! It's true that you can use a hairdryer to gently thaw the frozen section of the pipe, but it's best to have a professional check it out first—if a pipe has already busted and you just don't know it, thawing the ice inside will result in flooding.
Many thanks to my new best friend Justin, at JCA Mechanical Plumbing in Queens, who walked me through all these steps and made the very good point that attempting to thaw a frozen pipe can be a very bad idea indeed.