Washingtonians shivered through a second day of sub-freezing temperatures and biting winds Wednesday morning, giving the region its first true taste of winter this year.

Wind chills across the District, Maryland and Virginia made temperatures in the 20s feel more like the teens.

Plumbers were deluged with phone calls from homeowners experiencing frozen pipes, and local utilities were bracing for a flurry of water main breaks.

Water temperatures in the Potomac and other rivers that feed the area’s drinking water supply usually lag a day or two behind air temperatures, meaning water main breaks are likely to spike in the next couple of days, utility officials said. Sudden changes in water temperature cause already old, brittle pipes to weaken as they expand and contract.

“We’re asking for people’s patience,” said I.J. Hudson, a spokesman for the Washington Suburban Sanitary Commission (WSSC), which has 5,600 miles of water pipe in Montgomery and Prince George’s counties. “Things will start popping.”

The cold was blamed for a broken rail along Metro’s Green Line, causing trains on the route to share a track for nearly two hours Wednesday morning until the rail was replaced, said Dan Stessel, a spokesman for Metro.

But if the cold was an annoyance for most, in some cases it was life-threatening.

In Montgomery County, a cellphone tower repairman called 911 to say that he was too cold to get down, said Assistant Fire Chief Scott Graham of the county’s Fire and Rescue Service. The man exhibited “hypothermic” symptoms and was taken to a hospital, Graham said.

Shelters were filling up, and some localities opened extra facilities to house the homeless and allowed people to stay in them all day.

Fairfax County opened an additional shelter, for a total of six, and officials said residents can go to any open county building to stay warm, including libraries and government centers. No one will be turned away from a county shelter, said spokeswoman Merni Fitzgerald.

And in Arlington County, the A-Span emergency homeless shelter in the Courthouse area is “running above capacity,” said executive director Kathleen Sibert. That shelter has 73 beds, but on Tuesday night, 84 people needed housing. The extra 11 people were sent to Baileys Crossroads, where another shelter had room for them.

Because of the cold weather and high demand, the shelter’s normal 4 p.m. to 9 a.m. operating hours have been suspended and it is running round-the-clock, Sibert said. The daytime drop-in center in Shirlington has also experienced higher-than-normal usage, with 25 to 30 people staying there at a time. Volunteers have been calling or stopping by both places to donate hot food, cold-weather clothing and bedding, which is always in demand, Sacharko said.

In the District, several homeless people sought warmth at the Martin Luther King Jr. Memorial Library downtown. Some sat at computers, their bags at their feet, while others headed to the Art and Music room on the second floor to read. Different shelters had dropped them off there.

“When you’re homeless, you can’t dress for the weather,” said Shonice Garnett, 44, who has been homeless since she got laid off from her job as a District meter reader more than two years ago. “You can’t really carry a lot of bags or they throw them in the trash,” she said.

Shiela Mae, who sat across from her, said their shelter had filled up quickly the night before. “It’s a lot more crowded because normally they sleep outside,” she said.

Forecasts show no reprieve from the cold snap anytime soon. A slight warm-up is predicted for Thursday and Friday, and a slight possibility of snow Wednesday night could make things feel even more wintry.

The deep freeze, a result of cold air swept south from Canada, is stretching across the East Coast and the Upper Midwest, where temperatures in the teens would sound downright tropical. The Associated Press reported that Crane Lake, Minn., was among the coldest spots in the country, recording a temperature of 35 below zero Tuesday.

The weather is thought to have so far played a role in at least four deaths in the nation, according to the AP.

The bitter conditions were expected to persist into the weekend in the Midwest through the eastern half of the United States, said Shawn DeVinny, a National Weather Service meteorologist in suburban Minneapolis.

In Washington, people whose home towns are in far chillier regions shrugged off the bitter cold as an inconvenience that’s easily managed.

Gina Velosky, originally from New Hampshire, brushes D.C. winters off as “a joke.”

“Just dress like an onion and layer,” said Velosky, who has lived in the District for eight years. She had more advice for keeping warm: “This is good romantic weather. It gives you an excuse to cuddle. Also cuddle your dogs. They’re like little radiators. I have two.”

Some people said residents were lulled into thinking that the whole winter would be as warm as it has been until this week.

“As a people, I don’t think we’re prepared,” said Aimee Bottiaux, a Detroit native who manages an apartment building on Massachusetts Avenue. “It’s taken us by surprise because it’s been a very mild winter so far. It’s freaking people out.”

Bottiaux said she plans to combat the cold by avoiding it all together.

“You just don’t go outside when it’s like this,” she said.

Many normally crowded parts of the region were virtually empty. Old Town Alexandria had plenty of parking along King Street. The Mount Vernon bike trail, which parallels the George Washington Parkway and in warm weather is a commuter-and-recreation route as busy as the road itself, was nearly vacant from Old Town to Arlington Cemetery in late afternoon. Bicyclists and runners were far outnumbered by flocks of duck and Canada geese.

Smokers said they were taking fewer cigarette breaks, and vendors of Street Sense, a newspaper about the homeless, cut back their hours because passersby were reluctant to take off gloves to fish for change.

At Woodlin Elementary School in Silver Spring, outdoor recess was cancelled.

“This is like arctic air all of a sudden,” said Principal Sarah Sirgo said. “We have not built up for this.”

Many pedestrians said they were bundled up under several layers of clothing. Many clutched steaming cups of coffee or tea, whether they were drinking them or not.

Romeo Tchougoue, a doorman at the Madison Hotel for the past 15 years, is originally from Cameroon, where he said the average temperatures hover around 100 degrees year-round. His winter wardrobe here is built for warmth: long johns, hand warmers and a heavy coat.

“It’s a struggle and a challenge,” he said. “But thank God for that heat lamp.”

The District has a hot line that arranges transportation to shelters and the distribution of cold-weather items such as blankets, gloves and jackets. The number is  1-800-535-7252. Prince George’s County’s “Warm Nights” program places homeless people at area churches and provides them with meals. Call 1-888-731-0999 or 211 to be placed into the hypothermia program. And Fairfax County suggests that residents who see someone who might be at risk of hypothermia call the county’s non-emergency phone line at 703-691-2131.

Read more:

Latest forecast: Will bitter cold make way for snow?

Where heat is fleeing your house

Helping the homeless during cold front

Tips: How to stay warm

Share: How are you staying warm today?

Space heaters 101: Quiz and safety guidelines

Your photos of Washington’s freeze

Staff writers Tara Bahrampour, Mark Berman, Jeremy Borden, Rachel Karas, Michael Laris, Dan Morse, Corinne Reilly, Michael Rosenwald, Alex Rudansky, Katherine Shaver, Miranda S. Spivack, Donna St. George, Patricia Sullivan, Susan Svrluga and Matt Zapotosky and the Associated Press contributed to this report.