A broken water main in Elkridge disrupted one of Howard County's primary sources of water yesterday and triggered water-use restrictions in the populous eastern third of the county.

The county has banned outdoor use of water in an area that includes Columbia, Ellicott City, Savage, Elkridge and North Laurel and has asked residents to restrict unnecessary use of water indoors. Officials were hoping for weekend rain to discourage car-washing and lawn-watering.

By mid-afternoon yesterday, several of the county's big, free-standing water tanks were drained and the county had set up an emergency water-distribution center at Centennial High School in Ellicott City. Officials said they hope to have the pipe repaired by tomorrow morning and to lift restrictions Monday after water towers are refilled.

"This is the closest we've ever come to having a massive outage," said county utility chief Robert M. Beringer.

Because water was redirected from elsewhere in the county, none of the 40,000 homes and businesses in the affected area were reported to have run dry by late afternoon.

"Our main priority now is the hospital," Beringer said. He said water supplies are adequate at the Howard County Community Hospital in Columbia but expressed concern about other customers in that higher area of the county.

The 36-inch main, part of a 7.5-mile system that helps carry water from Baltimore to the growing eastern county, exploded with water around 4 a.m., taking a "serious swath out of the woods" off Elibank Drive and draining into the Rockburn Branch Creek, Beringer said. "It looks like a tornado went through the woods," he said.

Yesterday's water main break was the fourth in Howard since 1983. The 15-year-old pipeline system has been troublesome since 1984 and is being replaced at a cost of $7 million, Beringer said.

The concrete pipes are supposed to last at least 50 years, he said, but began to fail about seven years ago.

The manufacturer, GHA Lock Joint Inc., has been sued by several jurisdictions, including the Washington Suburban Sanitary Commission, Beringer said. The WSSC has had particular trouble with the company's pipes under Georgia Avenue -- a 48-inch main has created serious floods there -- and near Andrews Air Force Base, Beringer said.

Howard County is also contemplating legal action, he said.

County Executive Elizabeth Bobo said she can "count on our county's energy-conscious residents to cooperate" with the water restrictions.

Violators could have their water turned off and be charged for reconnection, officials said.