Investigators revealed on Saturday that not only had they narrowed the source of this week's massive electrical blackouts to problems in Ohio, but they had all but pinpointed its origin to three transmission lines operated in the northern part of the state.

"We are fairly certain" that the problem started in Ohio, Michael Gent, head of the North American Electric Reliability Council (search) said late Saturday. "We are now trying to determine why the situation was not brought under control."

Though that news came as a welcome relief to many across the country, it did little to calm concerns in the city of Cleveland where residents, faced with low water pressure, were still being told not to drink or cook with tap water without first boiling it.

Power was switched on Friday at the four pumps that provide water to 1.5 million people in the city and its suburbs. Still, bottled water became a precious commodity, and two dozen National Guard tankers began distributing emergency drinking water.

In Detroit, the failure of the state's electric pumps led to a run on gasoline with residents lining up to fill their containers.

Earlier this week, Michigan Gov. Jennifer Granholm (search) signed an executive order to expedite nearly 1 million gallons of gasoline from western Michigan to the Detroit area.

Granholm also warned residents of rolling blackouts (search) if energy was not conserved, while in Cleveland, upstate New York and New York City residents whose service had been restored saw it turned off again for that very reason.

In one positive development, Consolidated Edison announced that all power was restored to New York City on Friday night, just under 29 hours after the outage struck — outlasting the blackout of 1977 by almost four hours.

"We are 100 percent back," said Con Ed spokeswoman Joy Faber said. "Hundreds of employees are working around the clock and will continue to work through the weekend to stabilize the system and to try to prevent any further disruptions."

What Happened?

Meanwhile, the cause of the worst outage in U.S. history continued to elude experts. Investigators focused on a massive electrical grid that encircles Lake Erie (search), shuttling power from New York to the Detroit area, Canada and back to New York state. There had been problems with the transmission loop in the past, officials said.

"We will find out what caused the blackout and we'll deal with it. This was a wake-up call … for the need to modernize our electricity delivery systems," President Bush said from California Friday on a trip promoting his national park system. "The people in New York and in the Northeast and in the Midwest showed the great character of America under very difficult circumstances."

Although many people immediately suspected terrorism, an attack was quickly ruled out by Bush and other officials.

But the North American Aerospace Defense (search) command ordered two Air Force F-16 fighter jets to patrol the skies between New York and Washington as a precautionary measure. NORAD also put other aircraft on alert in eastern U.S. bases.

"I doubt the response would have been as good prior to Sept. 11," Bush said.

Homeland Security officials said all resources and available assets under their control were ramped up to be deployed Thursday night, but as of 1 p.m. Friday, only a request for a generator for New York City was made, Bush said.

Residents Get High Marks for Coping Skills

In New York City, Mayor Michael Bloomberg said he received a call from Bush offering congratulations on the city's handling of the crisis. Crime in the city was actually down overnight compared to an average evening, he said.

Video: New York Mayor Mike Bloomberg

"I think all New Yorkers have done their part," Bloomberg said. "If we compare this time to what happened in 1977, when there was chaos and crime, this time we saw compassion."

While the outage may not have sparked civil unrest, it paralyzed New York's crucial subway system and the two major commuter rail lines.

Just before 4 a.m. Thursday, the Metropolitan Transportation Authority said that all but a few of the city's subway lines were up and running.

In Ohio, most of the 1.4 million people affected by the blackout regained power by Friday afternoon. Nonetheless, Cleveland struggled mightily to provide residents with water for simple tasks like brushing teeth. There was not enough water pressure to create more than a trickle from taps.

"This is the crisis of a career for me," said Julius Ciaccia, Cleveland water commissioner, a 27-year employee. Cleveland officials, fearful of sewage flowing into Lake Erie because of the outage, closed the city's beaches.

In Connecticut, residents heard an emergency plea from the governor to cut back on power use after a state transmission line that feeds the southwest part of the state failed early Friday.

The call for conservation echoed across each state affected by the blackout. "Every light bulb matters today," said Long Island Power Authority (search) Chairman Richard Kessel. "If you don't turn them off, they will go off."

Despite plunging several of the nation's largest cities into darkness, the outage resulted in few reports of vandalism or increased violence. But there was at least one U.S. fatality: A 40-year-old New York man suffered a heart attack during an overnight fire.

In Canada's capital of Ottawa (search), police reported 23 cases of looting, along with two deaths possibly linked to the blackout — a pedestrian hit by a car and a fire victim. There were also reports of minor looting in Brooklyn and Detroit.

Officials in Michigan also blamed the power failure for a small explosion at a refinery about 10 miles south of Detroit. No injuries were reported, but hundreds of residents within a mile of the refinery were evacuated.

Officials warned Michigan residents that air conditioning and television could be out of commission until the end of the weekend.

Residents Ordered to Stay Home From Work

Bloomberg and Gov. George Pataki encouraged the locals to treat Friday as a 90-degree snow day — stay home from work and relax.

To reinforce their point, all state parks and beaches were open to the public for free. Pataki also demanded an investigation into what he called failures to improve the regional power system and prevent blackouts like those of 1965 and 1977.

"We have to know why this happened, how it happened," he said.

Cleveland workers were advised to stay home until noon on a day when temperatures climbed into the mid-80s. A few ignored the advice, strolling through near-empty streets.

"I have no water and no lights so I might as well come to work," said attorney Lori Zocolo, arriving at her downtown office at 5:30 a.m. in a T-shirt and shorts. Her biggest complaint: No water meant she couldn't brush her teeth.

Flights resumed Friday morning at Cleveland Hopkins International Airport as the airline business slowly returned. But despite the airlines' efforts, hundreds of flights were canceled nationwide.

At the New York area airports — Kennedy International, LaGuardia and Newark Liberty — planes were arriving and departing, but with unspecified delays. About 3,000 people were stranded overnight at Kennedy.

"They're trying to catch up," FAA spokeswoman Laura Brown said of the airlines.

Fox News' Bret Baier, Alisyn Camerota, Mike Emanuel and The Associated Press contributed to this report.