You can't fight fire with ice. That's a frozen fact that public safety officials are grappling with as extreme cold continues to grip Washington and much of the rest of the country this week. Broken water mains make fire hydrants weak. The water that firefighters carry on their trucks can freeze. Pumps lock up. Firefighters fall down.

"You see people trip on hose lines during sunny days, much less add ice, too," said Northern Virginia firefighter Chris Kamienski at Arlington County's Station 1 this week.

Plumbers have their own low-temp truisms (pipes burst), as do drivers (batteries fail), engineers (metal breaks) and doctors (joints ache from cold, bones crack from falls). It's all the toll of the cold. When the air gets down near zero, parts fail and people despair. From freight rails to frostbite, a deep freeze can mean deep trouble for a city — and a species — built to operate at more temperate temperatures.

Meteorology has become a doomsday science. Bomb cyclone? Polar vortex? Wind chills below zero? What happened to scattered flurries?

"When things get very cold, things change," John Jarrell, president of Materials Science Associates in Rhode Island said. "The nature of materials change, and the systems we've designed to operate at normal temperatures are stressed."

The evidence is everywhere. Crews are struggling to keep up with a record number of fractured water mains, with dozens reported in the Maryland suburbs. D.C. Water was working to fix 77 others while fielding more than 200 emergency calls a day tied to the frigid temperatures. Plumbers reported hundreds of calls for broken pipes at homes, apartments and office buildings, including a burst hot-water supply line earlier this week that spawned a small sidewalk glacier on L Street in downtown Washington.

More than 5,000 motorists in the District, Maryland and Virginia called for help before the worst cold weather even hit, mostly for dead batteries, flat tires and getting locked out of their vehicles, probably from leaving keys in their cars while warming them up, according to AAA Mid-Atlantic.

School systems in the area struggled to get their buses on the road, and nearly all, including the District and Montgomery, Prince George's, Fairfax, Loudoun, Arlington and Prince William counties, closed on Thursday. Montgomery announced a two-hour delay Friday, while Prince George's and Prince William said they would remain closed.

In Fairfax, about 200 of the district's nearly 9,000 bus routes had been delayed Wednesday or affected by buses with faulty batteries, freezing brake lines or other weather-related damage, officials said.

The cold played its winter wiles on bodies, too. Sometimes the bodies were complicit, such as the young people in Loudoun County who found themselves in hypothermic waters earlier this week after driving their SUV on the ice near Algonkian Park, or the skater who broke her wrist on the frozen C&O Canal.

But some bystanders were also felled by the freeze. Joints, particularly arthritic ones, grow achy in the extreme cold, possibly because the low barometric pressure causes tissues to swell. Sufferers of cold urticaria disorder get an itchy allergic reaction to cold air, and Raynaud's disease causes fingers and toes to go numb at times like these.

The deep cold literally takes the body outside its comfort zone, that core ideal around 98.6 degrees.

"The body is constantly trying to maintain the narrow range of temperatures where everything works optimally," said Ranit Mishori, professor of family medicine at Georgetown University School of Medicine. "When the body starts to lose heat, there is a cascade of responses."

The muscles contract and relax spasmodically — shiver — to generate heat, which requires increased glucose usage. Blood vessels constrict, helping to trigger an inflammatory response in the nostril lining that doctors call cold-induced rhinorrhea and to the rest of us is described as a runny nose.

The heart, too, has to work harder to keep a body warm, increasing the chance of a heart attack for those at risk, said Bradley Boyd, an orthopedic physician on call for Virginia Hospital Center's emergency room.

It was a remarkable bill of physical breakdown and cracked routines in a week without significant snow or high winds. It was pure cold air snapping bits off the built environment and the human psyche, even before the bomb cyclone detonated and the most frigid air of the season rushed into the region Thursday night. This winter, still in its infancy, was already wearing on the local spirit.

"I am so tired of being cold — already!," lamented Julie Ann Pixler, a former C-SPAN producer, on the Capital Weather Gang's Facebook page.

"Same," seconded reader Arielle K. Masters.

The main cold-weather culprits, according to Jarrell, are the facts of physics. Extreme cold causes most materials — such as plastic pipes and metal parts — to become less flexible and more brittle. If your Metro car has to single-track around a cracked rail, you can impress your fellow passengers by blaming the dreaded "ductile to brittle transition."

Water, on the other hand, swells when it freezes, forming a perfect pipe-breaking scenario, especially when the temperatures are cold enough to penetrate deep into the ground where the usually snug pipes are buried.

Chemical reactions, meanwhile, tend to slow in the cold, weakening car batteries. Oil becomes thicker and frozen metal parts shrink at different rates — think about aluminum pistons sitting in tight iron cylinders — making engines harder to budge for those already feeble batteries. Nothing is quite normal.

Think of a Milky Way bar, Jarrell suggests. Break it in two at room temperature and its various layers will stretch and ooze at different delicious viscosities. But pull it from the freezer and "you can snap it like a candy cane," Jarrell said. "At low temperatures, things begin to act in ways contrary to what we're used to."

Kamienski, along with firefighters across the region, know how tricky it gets with winter and water. He points to the "pump shift" knob below the steering wheel of Engine 101, the controls he'll use to keep the water moving through the truck's 750-gallon tank and 30-gallon pump to keep it fluid. Elsewhere, the truck's cold weather kit includes a plastic sled to pull injured people over frozen ground, snow shovels and cat litter to spread over slippery patches.

Ice can lock firefighters' extension ladders up. Frozen hoses refuse to coil. But the calls keep coming. An overhead screen flashed the details of a medical call. In his rush to respond, Kamienski almost left his new insulated Yeti mug behind.

"Don't want to forget my Christmas gift," he said.

At the Washington Aqueduct, workers battled the freezing Potomac by hand, like ancient whalers, using steel rods to punch through ice two inches thick near the intake pipes that supply the District and parts of Northern Virginia with drinking water.

Crews had scrambled to break up the bergs Sunday after ice began to block the pipes and the reservoir level dropped, said Thomas Jacobus, the aqueduct's general manager. "Ice eater" machines churned the water with propellers to keep more ice from forming, he said.

With even lower temperatures forecast, the aqueduct had a crane and wrecking ball standing by to break up large chunks that could overwhelm the intake.

Jacobus said aqueduct officials couldn't remember another stretch when night temperatures dipped into the single digits and daytime temperatures didn't reach above freezing. "This is what you expect in Iowa, for goodness sakes," Jacobus said. "Nothing has a chance to warm up to defrost itself."

Workers have wrapped black plastic around equipment to try to hold in heat and brought in portable heaters to keep smaller pipes from freezing. The extreme cold also makes chemical reactions in the water-treatment process sluggish. Crews are adding more coagulants to get dirt to settle and keeping an eye on chlorine levels to make sure the chlorine has enough time to kill bacteria.

"Our systems are taxed," Jacobus said. "We'll be okay, but we are right at the edge of the capabilities of our heating systems. They're not built for this."

And neither are we.

Katherine Shaver, Luz Lazo, Debbie Truong, Perry Stein, Lori Aratani, Michael E. Ruane and Dana Hedgpeth contributed to this report.