A ‘catastrophic’ rupture hits region’s water system Nearly 2 million residents of Greater Boston lost their supply of clean drinking water when a huge pipe abruptly burst yesterday, prompting authorities to declare a state of emergency and to impose a sweeping order for homeowners and businesses to boil the untreated water now flowing from their tapsA ‘catastrophic’ rupture hits region’s water system

Many questions remained unanswered.

Officials said they did not know how long it would take to restore clean drinking water to the region, but Laskey said he hopes it will be “days, not weeks.’’

Officials also said they did not know what caused the relatively new seven-year-old steel pipe to break 20 feet underground, near Recreation Road by the intersection of the Massachusetts Turnpike and Route 128.

Officials shut off the water supply into the pipe at about 6:40 p.m. Soon after, engineers discovered rubber gaskets floating above the leak, leading them to theorize that the pipe had ruptured at a sleeve connecting sections of the pipe.

By 10 p.m., Laskey said engineers could see into the pipe. It was still half-full with water. But he said he was encouraged that the problem might be solved relatively soon because the sleeves could be fixed more easily than the steel pipe.

“In a sense, it’s the most vulnerable point in the system,’’ said Tom Baron, an independent water systems engineer who formerly worked for the water authority.

Officials said that if they cannot repair the pipe with a temporary patch, a new custom-made pipe might have to be built. Officials had been building a backup system for Greater Boston’s drinking water system, but it is three or four years from completion. Before water was shut off to the ruptured pipe yesterday, brown water had been roaring from a massive crater in the ground, sending more than 8 million gallons an hour rushing down a hill into the nearby Charles River.

The state Department of Conservation and Recreation said the millions of gallons pouring into the river would not be a problem, even as the river’s elevation rose by 8 inches in some locations and its flow nearly doubled in a matter of hours.

“Our dams can handle this,’’ said Wendy Fox, a spokeswoman for the agency.

But Nigel Pickering, senior engineer and watershed modeler for the Charles River Watershed Association, warned that the water entering the river from the break could stir up sediment, harming fish. Laskey said it did not appear that sediments had been kicked up as of last night.

Authorities said that contractors and engineers would know more about what went wrong today, when they have a chance to better inspect the pipe.

“I really don’t want to speculate,’’ Laskey said at the scene of the break. “We’ve got to get there to know.’’

Not every community was affected. Cambridge, for example, has its own water supply.

And water authority spokeswoman Ria Convery said that the authority, working with the Boston Water and Sewer Commission, was able to reconfigure the water pipe lines in the Longwood Medical Area. That temporary fix allowed four major hospitals in the area — Children’s Hospital, the Dana-Farber Cancer Institute, Beth Israel Deaconess Medical Center, and Brigham and Women’s Hospital — to go about business as usual, without having to resort to bottled water, she said.

Eric Moskowitz and John M. Guilfoil of the Globe staff contributed to this report.