A 54-inch water pipe breaks in Capitol Heights, Md., in January 2011. (Tracy A. Woodward/The Washington Post)

Topsy-turvy temperatures in November and a cold snap in late December led to a spike in water-main breaks across the Washington region, but a relatively warm year overall helped keep the total number of breaks for 2012 to the lowest count in six years.

By year’s end, 2,211 pipes had broken or leaked in the District and Fairfax, Montgomery and Prince George’s counties, according to figures provided by local utilities. That amounted to 20 fewer breaks regionwide than in 2011 and nearly 900 fewer than in 2007.

Of course, that didn’t lessen the misery for people who were stuck in traffic backups when bursting mains tore open roads or who were temporarily left without drinking water or flushing toilets.

The new year’s frigid weather is also weakening pipes, including a broken main that snarled Thursday morning’s commute on Wisconsin Avenue through Chevy Chase.

“It all amounts to any significant shift in weather,” said I.J. Hudson, a spokesman for the Washington Suburban Sanitary Commission. “Any change in temperature dramatically increases stress on pipes.”

Washington area water main breaks

Water utility officials say that they welcome fewer breaks overall but that it is too early to declare a trend. Although local utilities have stepped up the replacement of aging pipes in recent years, officials also say it is too soon for those efforts to be having an impact.

Several theorized that relatively mild autumns and winters in the past couple of years have prevented a repeat of the spike seen in 2010, when nearly 3,000 mains across the region burst or sprung a leak during a particularly cold winter.

The difference in the number of pipe breaks from one year to the next, utility officials say, can boil down to a few days of up-and-down water temperatures that cause old, weak pipes to expand and contract until they snap.

DC Water, which serves 600,000 residents, had 282 breaks last year, down from 351 in 2011.

“The rehab work is probably helpful at the margins, but the most helpful factor is the weather,” said George Hawkins, general manager of DC Water.

In November, the temperatures that caused people in the Washington area to bundle up one day and break out shorts the next caused 316 breaks in WSSC pipes, the second-highest tally on record for the month. One of the breaks, in Largo, left 600 homes under a precautionary boil-water advisory over the Thanksgiving holiday weekend.

But overall, WSSC’s 1,602 breaks for the year gave the utility its second-lowest annual count since 2006.

“One or two years doesn’t make a trend, especially when you look at the weather,” said WSSC spokesman Jim Neustadt. “We’re happy people are not as inconvenienced by water-main breaks, and we hope our work has had some effect on that, but it’s too early to spot a trend.”

Neustadt said WSSC engineers predict that it will be 10 to 12 years before any reduction in pipe breaks can be attributed to stepped-up replacements and inspections. Even the 170 miles of pipe replaced in the past seven years — at an average cost of $1.4 million per mile — covers only 3 percent of the WSSC’s 5,600-mile system of water pipe.

“We’re making great progress, but when you look at the number of miles done in the last seven years, it’s a drop in the bucket compared to where we need to be,” Neustadt said.

The more aggressive pipe rehabilitation and replacement programs are coming at a cost to customers. After almost a decade with no rate hikes or annual increases at 2 or 3 percent, WSSC bills have grown by almost 50 percent over the past six years. DC Water’s residential customers are paying an average $71 monthly, up nearly 40 percent from an average $51 monthly five years ago.

The region’s crumbling pipes are a sign of the nation’s aging infrastructure. Unlike bridges and roads, pipes are buried out of sight, making them particularly easy to neglect, experts say, and many of those buried in the post-World War II development boom years are beginning to show their age.

A 2011 study commissioned by the American Water Works Association found that replacing the deteriorating pipes while keeping up with new population growth would cost utilities nationwide more than $1 trillion over the next 25 years.

Almost one-third of WSSC mains are more than 50 years old, while DC Water’s mains average 78 years. Two percent of the District’s water mains, particularly in older areas of the city north and west of the White House, date to the late 1800s, while about five miles were buried before the Civil War, Hawkins said.

While sewer pipes can be just as old as water mains, utility officials say, they are less susceptible to breaks because they are not under constant stress as the heavily pressurized water mains are.

While the District’s pipes are, on average, older than those in the suburbs, the WSSC has a far larger system — about 4,250 more miles of water pipe than the District.

Fairfax Water, which serves nearly 1.7 million people in Fairfax County, Loudoun County, Prince William County and Alexandria, is also large — 3,280 miles of water mains. But its pipes are relatively young, with more than half less than 30 years old.

Fairfax Water had 327 breaks last year, up slightly from 307 in 2011.