Even while the exact cause remains unknown, a deadly blast that leveled two Manhattan buildings served by a 127-year-old gas main has provided a jarring reminder of just how old and vulnerable much of the infrastructure is in New York and many other cities nationwide.

A detailed report issued only a day before Wednesday’s explosion in East Harlem estimates that $47 billion is needed for repairs and replacement over the next five years to spare New York from havoc.

Nationally, the projected bill – for bridges, highways, mass transit and more – is almost incalculable. Just upgrading the nation’s water and wastewater systems is projected to cost between $3 trillion and $5 trillion over the next 20 years, according to the Competitive Enterprise Institute, a conservative Washington think tank.

Politicians often shy away from blunt talk about infrastructure, but it was in the spotlight Thursday as investigators sought to determine how and why a suspected natural gas leak triggered the explosion that destroyed two apartment buildings, killed at least seven people and injured more than 60.

19TH-CENTURY PIPING

Whether an 1887 cast iron gas main serving the buildings was a factor remained unknown Thursday. But it was nonetheless upsetting for New Yorkers to be reminded that Consolidated Edison, the natural gas supplier for East Harlem and much of the rest of New York, makes extensive use of 19th-century piping.

“I can’t imagine how we can have pipes underground in New York that were put in there in the 1800s,” said U.S. Rep. Charles Rangel, a Democrat who represents Harlem in Congress.

“You know we talk about infrastructure but the whole damn city is falling apart,” Rangel said.

Mayor Bill de Blasio, who took office on. Jan. 1, says the burden lies with the federal government to provide more aid to U.S. cities for repair and replacement of aging infrastructure.

“The broader infrastructure challenge is something we address every single day with the resources we have, but that is a tough battle considering we are not getting some of the support that we deserve,” he said.

Just Tuesday, a New York-based public policy think tank, the Center for an Urban Future, released a detailed report about New York’s infrastructure, saying it posed problems that “could wreak havoc on the city’s economy and quality of life” if left unchecked. It estimated that $47.3 billion would be needed over the next five years to make crucially needed repairs and replacements.

The report’s author, Adam Forman, noted that Michael Bloomberg, New York’s mayor from 2002 through 2013, oversaw significant new construction, but said the city lost ground during that period in terms of infrastructure maintenance.

“Repairing and replacing aging infrastructure is not glamorous, but it’s critical,” said Forman, who suggested that the East Harlem explosion might be the sort of catalyst needed to gain politicians’ attention.

DETAILS OF REPORT

According to Forman’s report:

More than 1,000 miles of New York City water mains are 100-plus years old. The typical water main is 69 years old, and there have been more than 400 water main breaks annually in recent years.

More than 160 bridges across the city’s five boroughs were built more than a century ago, and 47 bridges in 2012 were deemed structurally deficient and prone to collapse.

–The subway system abounds with signals that have exceeded their 50-year useful life, slowing the movement of trains and forcing maintenance workers to build their own replacement parts because manufacturers no longer make them.

SIMILAR PROBLEMS ELSEWHERE

Similar problems beset cities across the United States.

According to the Department of Transportation, New York City still uses about 3,000 miles of decades-old cast-iron gas pipe, Boston about 2,000 miles and Philadelphia about 1,500 miles.

In addition to cost, one deterrent to massive pipe replacement is disruption to traffic on the streets overhead.

Forman acknowledged this was a challenge in a crowded city such as New York, but said new technologies were being developed to reduce the need for cutting streets open.

Overall, Forman’s report said, it’s in New York’s self-interest to invest in upgrades of all types.

“Too much of the city’s essential infrastructure remains stuck in the 20th Century – a problem for a city positioning itself to compete with other global cities in today’s 21st Century economy,” he wrote.