A pipe burst. What do I do right now?

Find the main shutoff valve. It’s usually where the water line enters the house: in the basement or crawl space along the front wall, near the water meter, or in a utility closet. Turn it clockwise until it stops.

Then open a cold tap at the lowest point in the house to drain the water left in the pipes.

Don’t walk into standing water if outlets, cords or appliances are in it. If you can reach the breaker panel without standing in water, switch off power to the wet areas. If you can’t, wait for an electrician or the utility.

Watch the ceiling under the leak. A bulging, sagging ceiling can hold a lot of water; keep people out from under it.

Move what water hasn’t reached yet, and lift what it has.

Take photos and video of the water, the damage and the pipe before anything is moved or thrown away. If a plumber cuts out the broken section of pipe, keep it. Keep receipts for anything you spend because of the damage.

Water wicks up drywall, soaks into insulation and spreads under flooring, far past what you can see. According to the EPA, if wet materials are dried within 24 to 48 hours, in most cases mold will not grow.

“Looks dry” isn’t dry. Professional drying uses air movers, dehumidifiers and moisture readings to confirm walls and floors are actually dry before the equipment comes out.

Pipes in exterior walls, crawl spaces, attics and unheated basements are the ones that freeze. Water expands by about 9% when it freezes, which is enough to split a pipe; the leak usually shows up when it thaws.

To prevent it in a cold snap: keep the heat on, even when you’re away; let a faucet on an outside wall drip; open the cabinet doors under sinks so warm air reaches the pipes; and disconnect garden hoses before winter.