At first glance, the pizza-size hole that popped open when a heavy truck passed over a freshly paved District street seemed fairly minor.

Then city inspectors got on their bellies with a flashlight to peer into it. What they discovered has become far too common. A massive 19th-century brick sewer had silently eroded away, leaving a cavern beneath a street in Adams Morgan that could have swallowed most of a Metro bus.

It took three weeks and about a million dollars to repair the sewer, which was built in 1889.

Time and wear “had torn off all the bricks and sent them God knows where,” said George S. Hawkins, general manager of the District of Columbia Water and Sewer Authority. “We have to find them and see if they’re plugging up the system somewhere farther down the line.”

If it were not buried underground, the water and sewer system that serves the nation’s capital could be an advertisement for Band-Aids. And it is not much different from any other major system in the country, including those in many suburbs and in cities less than half as old as Washington.

(Vote: How should we fix the systems? )

Although they are out of sight and out of mind except when they spring a leak, water and sewer systems are more vital to civilized society than any other aspect of infrastructure.

Rapidly deteriorating roads and bridges may stifle America’s economy and turn transportation headaches into nightmares, but if the nation’s water and sewer systems begin to fail, life as we know it will too. Without an ample supply of water, people don’t drink, toilets don’t flush, factories don’t operate, offices shut down and fires go unchecked. When sewage systems fail, cities can’t function and epidemics break out.

“All the big cities have these problems, and to me it’s the unseen catastrophe,” Hawkins said. “My humble view is that the industry we’re in is the bedrock of civilization because it’s not just an infrastructure that is a convenience, that allows you to get to work faster or slower. At least with bridges or a road, people have some idea of what it is because they drive on them and see them. ”

And just like roads and bridges, the vast majority of the country’s water systems are in urgent need of repair and replacement. At a Senate hearing last month, it was estimated that, on average, 25 percent of drinking water leaks from water system pipes before reaching the faucet. The same committee was told it will take $335 billion to resurrect water systems and $300 billion to fix sewer systems.

There is no better illustration of the looming national crisis than the District’s system.

The average D.C. water pipe is 77 years old, but a great many were laid in the 19th century. Sewers are even older. Most should have been replaced decades ago.

Emergency crews rush from site to site to tackle an average of 450 breaks a year.

Raw sewage flows into the Potomac, the Anacostia and Rock Creek whenever it rains hard — hundreds of times a year — an annual flush of about 3 billion gallons, according to D.C. Water.

Firefighters are equipped with computerized cue sheets to tell them which of the 9,157 hydrants in the District have enough water pressure to put out a fire.

The average water and sewer bill has gone up about 50 percent in just four years, to $65 a month for single-family homes. Unless there is federal regulatory relief, it may climb to $100 a month by the end of the decade.

The decrepit system has 1,300 miles of water pipe and 1,800 miles of sewers. The water pipes are being replaced at an average of 11 miles a year. At that rate, replacing them all will take more than 100 years.

There’s no money to do it any faster. And, Hawkins says, “if you did it much faster than that, you could paralyze the city in terms of traffic.”

* * *

A snowstorm had turned the District into a ghost town a couple of years ago when Hawkins trudged through the snow to check a break in a water main at 21st Street and New Hampshire Avenue.

The intersection isn’t far from several embassies, and a few foreign visitors came from a hotel on the corner to watch as snowplows dug down to find the leak’s source. Hawkins recalls telling the visitors that the old mains under New Hampshire Avenue burst fairly often. “They said: ‘You have pipes that were put in in the 1860s? We thought we had it bad in Ghana!’ ”

* * *

The good news? The District’s pipes are being replaced twice as fast as the average in other major water systems in America.

The gargantuan numbers tossed around during December’s Senate hearing as the cost of saving the country’s water and sewage systems have no more promise of connecting with the public than has the $7 trillion that transportation experts say should be spent to resurrect roads, bridges, aviation and transit in the next decade.

About $9.4 billion more per year is needed for water and sewer work between now and 2020, according to a study released last month by the American Society of Civil Engineers. Without that, many Americans should prepare for regular disruption of water service and a jump in contamination caused by sewage bacteria, the study said.

The price of water, always far below commodities like electricity and gasoline, can be expected to rise dramatically as the demand taxes the systems that deliver it, analysts agree.

Nationwide, an estimated 1.7 trillion gallons of water leaks from pipes each year before it can be put to use. About 900 billion gallons of raw sewage flows into waterways.

Those leaks and untreated flushes aren’t just a problem in creaking Eastern cities that date to colonial times. Oklahoma, which didn’t become a state until the 20th century, has estimated it needs to invest $82 billion in water and sewer infrastructure over the next 50 years.

“I remember when they used to consider us out in the newer states like Oklahoma as not having the infrastructure problems of older states,” Sen. James M. Inhofe (R-Okla.) said, “but that’s not true anymore.”

Although suburbs that have appeared or expanded since World War II have newer systems, they’re showing age. Even in this relatively mild year in which there have been fewer breaks — more mains break when there are severe temperature swings — the Washington suburbs have had problems. There have been more than 1,440 leaks or breaks in Montgomery and Prince George’s counties this year. Fairfax County has had 300.

“People count on turning on the faucet and having clean water come out,” said Sen. Benjamin L. Cardin (D-Md.), chairman of the subcommittee on water. “Our nation’s water infrastructure is reaching a tipping point.”

But with the economy sputtering and Congress eager to slash a burgeoning deficit, selling Americans on the need to pay billions more in water bills or taxes to salvage a system they didn’t even know was breaking may be impossible.

“The customer base really doesn’t know,” Hawkins said. “Like when I turn on the faucet, what on Earth is needed to deliver that water? It’s like magic. And then it goes down the drain. It’s like magic again.”

* * *

Hawkins was awakened on a Friday night in October 2010 to news that water was erupting all over the place at Constitution Avenue and Ninth Street.

“When a water main breaks, all hell breaks loose because it’s under such high pressure,” he said. “We dug an original hole that wasn’t in the right place because at first you can’t really tell” where the break is — the water can work its way to the surface through any fissure.

Pressure from the 24-inch main buckled the pavement a foot high. Water flooded the basement of the Department of Justice. The Smithsonian’s National Museum of Natural History had to shut down the next day.

The torrent was unleashed by a water main that had been installed in the 1890s, when Grover Cleveland lived a few blocks away in the White House.

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