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Judging by the pipes and plumbing fixtures inside the E.W. Berger & Bros. warehouse in New Jersey, the slumping global copper market has more to worry about than just weakening demand from China.

E. W. Berger has cut monthly purchases of copper products to 5,000 pounds from 20,000 pounds a decade ago. While the cost of the metal has dropped, more clients prefer plastic, which is even cheaper, owner Jay Richman said.

Demand for copper in the U.S., the second-largest user, has plunged by more than a quarter in the 10 years through 2014, including a 55 percent plunge in tubes and pipes, the Copper Development Association estimates.

From plumbing to communications to electronics, traditional copper uses are losing out to lower-cost or better-performing substitutes.

That's muddying the demand outlook as economic growth slows in China, which accounts for 45 percent of demand and helped send prices to a record in 2011.

Now, the metal has dropped in value for three straight years and in January slid to the lowest since 2009, as mine owners failed to cut output enough to avoid a surplus.

"It's a dramatic shift," said E.W. Berger's Richman, 65, who has been selling plumbing supplies in Weehawken for four decades at the business founded by his father. "People are continuously changing and trying to find the best way and cheapest way to do it."

Copper has slumped as global production expanded faster than demand, following a so-called commodity super cycle that marked a decade of rising prices and consumption.

Output is still increasing, with more than 4.5 million metric tons of new capacity planned to come online over the next four years, according to Bloomberg Intelligence estimates. Production has exceeded demand in 18 of 19 months through January, according to the World Bureau of Metals Statistics.

The copper surplus will last through 2019, analysts at Goldman Sachs Group Inc. wrote in a Feb. 8 report. The New York-based bank predicted prices on the London Metal Exchange will drop to $4,000 a ton over the next 12 months, compared with $4,949.50 on Wednesday.

While mines have continued to expand after copper topped $10,000 in 2011, the incentive that created for consumers was finding cheaper alternatives. And even though prices have come way down, demand hasn't come back.

"Substitution happens in every super cycle," said John LaForge, the Sarasota, Florida-based co-head of real-asset strategy at Wells Fargo Investment Institute, which manages $1.7 trillion. A surge in prices "corrects everything, but what survives and what comes out of the back-end isn't always the same," he said.

In the U.S., annual consumption of refined metal has fallen in five of the past 10 years and is 21 percent lower over that period, at 1.79 million tons, according to the World Bureau of Metal Statistics.

Of the 18 end-use markets tracked by the Copper Development Association, the only gains from 2004 to 2014 were in power cable, automotive wire and transportation equipment.

Excluding Asia, the combined consumption in the rest of the world shrank 20 percent in the past decade, data compiled by Bloomberg Intelligence shows.

Even in China, Goldman Sachs is predicting zero growth this year. The Lisbon-based International Copper Study Group on March 10 forecast "essentially flat" global usage this year for refined copper, excluding stockpiling, even as output rises, creating a surplus through next year.

Not everyone is so concerned about prospects for consumption. In March, hedge funds have begun betting on price gains, a switch from December, when they held the largest net-short position in New York futures since April 2013.

Prices are headed for a second straight monthly gain, the longest rally in almost a year, amid speculation that low interest rates will spur purchases of all sorts of raw materials that have gotten cheaper.

The move to alternatives is "not strong enough of a threat to really bring down global copper demand to a negative level," said Dane Davis, an analyst at Barclays Plc, who is the most-accurate copper forecaster tracked by Bloomberg in the quarter ended December 2015. "We're not going to start using less copper on a total basis as a result of this."

Still, some industries are seeing big declines. In telecommunications, where copper was used for more than a century in phone lines, global demand slid 65 percent in the decade through 2015 as the metal wire was replaced by fiber-optic cable, according to researcher CRU International Ltd.

Verizon Communications Inc., the largest U.S. wireless provider, said it has switched more than 1 million customers since 2012 from copper to fiber-optic cable, which can handle more data and requires less maintenance.

AT&T Inc. said its upgrade helped give users access to Internet speeds of up to 1 gigabit per second in more than a million locations.

"Most new network construction will use fiber" instead of copper, said Richard Mack, an analyst at CRU's wire and cable team. "Much of the demand for fiber in the world market is for upgrading the fixed line from copper to fiber to achieve faster Internet service."

The switches aren't much different for the plumbing business. At an 80-home development in East Orange, N.J., E.W. Berger is supplying the building contractor with 2,000 feet of polyethylene pipes — known as pex — instead of 2,000 pounds of copper tubes.

"It's hard to see where the increase in demand for copper will come from," said Frances Hudson, an Edinburgh-based global thematic strategist at Standard Life Investments, which oversees $393 billion.

"There isn't another China waiting in the wings that is going to need massive amounts of industrial metals," she added. "The rest of the world that will develop might need different kinds of infrastructure, but less physical infrastructure."