ROBINSON TOWNSHIP, PA., JAN. 5 -- Sandy Snyder awoke today in this community cradled by three rivers, turned on the kitchen faucet and found not a drop to drink.

Her Pittsburgh suburb of 20,000 people was bone dry three days after a storage tank owned by Ashland Oil Co. ruptured in Floreffe, 25 miles south and upstream of here, spilling more than 1 million gallons of diesel fuel into their water source -- the Monongahela Rivers.

Pittsburgh, which drinks from the Allegheny River, was spared. The Allegheny meets the Monongahela in downtown Pittsburgh to form the Ohio River, which was carrying much of the oil into West Virginia.

As Snyder and residents of other Allegheny County communities ringing Pittsburgh filled vessels from water tanks supplied by the National Guard, Ashland's crew of more than 100 continued its cleanup. The spill was expected to reach Wheeling, W.Va. -- 60 miles from its origin -- Wednesday and may reach the Mississippi River, federal officials said.

Although the cause of the spill remains uncertain, company chairman John Hall said tonight that the 40-year-old, 4 million-gallon tank was erected in fall 1986 and filled nearly to capacity Saturday without local permits and without the standard tests for such containers.

"We're very sorry that the citizens of Pittsburgh have suffered any inconvenience," Hall said at a news conference, pledging to complete the cleanup that may take several weeks and cost more than $15 million.

Hall said the tank was moved from Cleveland and reassembled "on verbal communication with the authorities . . . . I do not know if we were in compliance with the law or not." Fuel-tank construction in Pennsylvania must be approved by the county fire marshal, and Allegheny County Fire Marshal Martin Jacobs told The Associated Press today that he knew of no verbal approval for the ruptured tank.

Ashland normally tests a tank for leaks by filling it with water. Hall said the Floreffe tank, 48 feet high, was tested with five feet of water. It collapsed Saturday as it was being filled for the first time, sending more than 3 million gallons of diesel fuel gushing into the surrounding containment dike.

The force of the rupture sent about 1 million gallons splashing out of the dike, built at 110 percent of the tank's capacity, and into the river, Hall said. Emergency officials estimated today that only 100,000 gallons have been siphoned out of the water.

"In hindsight, one might question the use of 40-year-old steel," Hall said tonight. "We might have been more persistent in getting our permits. I would have preferred to use water-testing methods. But there's no evidence that making a different decision on any of these issues would have prevented failure of the tank."

More than 750,000 people get their water from the Monongahela.

Western Pennsylvania Water Co., largest of three suppliers in the area, closed one of its intake plants Sunday as the oil spill moved downstream. That plant supplies 500,000 residents in Allegheny County, who have been using the water that was left in their pipes.

Their major problem today was low water pressure. But 60,000 people living in smaller communities at the end of West Penn's distribution system were down to their last drops of water today. "What people were living on was stored water, and now we're totally out," West Penn spokesman Denis Casey said.

West Penn's second intake plant serves Washington County, southwest of the spill.

By connecting Pittsburgh fire hydrants to some of its nearby hydrants with fire hoses, West Penn has been borrowing about 3 million gallons of water a day for Allegheny Country. West Penn officials said a pipe being installed to augment the loan would not operate until Wednesday.

In Robinson Township and North Fayette -- served, like many small communities in the county, by a municipal authority with much smaller reserves -- the drought began Monday night. Water tanks were hauled to a school and a home for the retarded. The fire department put neighboring stations on alert for possible help in combating fires. Public schools and most businesses, motels and restaurants closed, freeing residents to flock to the water trucks provided by the National Guard at two 24-hour depots.

"They're bringing in sprinkling cans, coolers, five-gallon jugs, almost anything that can carry water," said Ron Marko, who was overseeing the tanks at a school bus garage. "One guy came in and took out 150 gallons in a plastic garbage can."

One of Marko's customers was Snyder, a government typist, who discovered the outage this morning as she slid her tea kettle under the kitchen faucet. Unable to bathe, wash her clothes, steam vegetables or flush the toilet, she is learning the luxury of running water.

"We're so used to turning on the tap and water being there," she said. "I'll never take it for granted again."

For Joseph Ciallelli, a contractor, the experience has recalled stories by his grandmother who had drawn water from a natural spring. "But that was in Italy a long time ago," he said, "and this is Pittsburgh today."

At the Stop & Go shop, in the shadow of the township's empty red-and-white water tower, clerk Tony Salvie reported sales of all but 50 of the 250 cases of distilled water specially ordered in the last 48 hours.

"God knows, by tonight we'll be out," he said. "Then, they'll have to drink beer."

The township's supplier is trying to borrow 30,000 gallons per day of water from a neighboring company, but the loan would make only a small dent in the 1-million-gallon daily demand. Officials believe full service may be weeks away -- and only after the oil is captured or carried away by the current.

Here in Pennsylvania, they coped with the oil. Downstream, they waited for it. City crews in Wheeling began installing a six-inch pipeline from Martins Ferry, Ohio, to borrow as much as 1 million gallons of water a day if the spill contaminates its water supply. A smaller line would import water from Bridgeport, Ohio.

Wheeling Assistant City Manager Nancy Vapner told The Associated Press that Ashland barges were being towed to the mouth of Wheeling Creek where it empties into the Ohio, in expectation of pumping another million gallons into the city's water system each day. She said the city of 42,000 uses about 7.5 million gallons a day.

Long-term exposure to diesel fuel, a complex mixture of hydrocarbons, has been associated with cancer, suppression of the immune system and gene mutations in humans or laboratory animals. The short-term effects can include nausea, dizziness and headaches.

Dead fish and ducks have been found along the river, and Environmental Protection Agency officials said they were assessing the oil's impact on wildlife.