Electrically powered commuter trains ran on time and stop lights kept traffic running smoothly Monday as millions of people headed back to work for the first time since the big blackout (search). In Detroit, residents returned to drinking straight from the tap.

Power plants (search) knocked out by the outage were coming back on line, increasing the electricity flow in time for the high power demand of the start of the work week.

And relatively cooler weather was forecast, with highs only in the upper 70s over the Northeast and low 80s in parts of the Great Lakes (search) region.

However, utilities in the eight-state region hit by Thursday's blackout — the largest in U.S. history — warned that they weren't out of the woods yet.

New York's Consolidated Edison (search) asked customers to conserve power during Monday's usual spike in demand. "We're still stabilizing our system," spokeswoman Joy Faber said.

The North American Electric Reliability Council announced late Sunday that the power grid was operating reliably again, with all but one transmission line back in service. On Monday, spokeswoman Ellen Vancko said the council had no updates and had no immediate plan to release any updated information.

A reliability council e-mail statement said the grid was expected to operate reliably barring unforeseen events.

From Michigan to New Jersey, motorists and police reported no power-related problems with the Monday morning commute.

NYC Transit officials said subways in the nation's largest mass transit system, carrying 5 million riders daily, were running on schedule. Officials of the Metro-North and Long Island Rail Road systems serving the suburbs said their trains were running on or close to schedule.

At New York's Grand Central Terminal, banker Jonathan Greenman said he had a problem-free trip in from Rye, N.Y. "I haven't been worried since I found out the trains started running again this weekend," he said. "I feel things are back to normal now."

"We're off to an auspicious start," Dennis Selmont said at the train station in Milford, Conn. "There's no one standing on the platform telling us there are no trains."

New York Mayor Michael Bloomberg was upbeat.

"The subways are working, the buses are working," Bloomberg said on cable news channel NY1. "It's a Monday morning in New York; that's what you'd expect."

Wall Street got back to normal, although trading was light since there was little economic or earnings news to influence the market.

Lingering concerns about water safety eased Monday with the announcement that Detroit residents would no longer be asked to boil their tap water. A similar boil order in Cleveland was lifted Sunday evening.

In Canada, where a large part of Ontario lost power, government offices offered only essential services and authorities pleaded with businesses, industry and the public to reduce electricity use by 50 percent. "We currently do not have enough generation back on line to see us through a regular weekday," Premier Ernie Eves said.

The NERC said it didn't foresee any need for similar public appeals in the United States.

Still, the power system remains "a little delicate," said Long Island Power Authority chairman Richard Kessel. "We ask that people don't go crazy using electricity on Monday," he said.

Ken Klapp of the New York Independent System Operator said the state was expected to have more than enough power to meet Monday's estimated peak load of 25,000 megawatts.

The restarting of New York's nuclear power plants, which at full capacity can provide 5,000 megawatts, would be a "big help" in meeting the increasing demand, Klapp said. Six of the nine U.S. nuclear power plants that shut down in the blackout are in New York; all but one were scheduled to be up and running by Tuesday night.

The blackout cost the economy of New York alone hundreds of millions of dollars.

"It's serious," said Pando Andonopulo, who has run the Ninth Avenue Cheese Market in New York for 30 years and said he lost hundreds of pounds of cheese, prepared salads and sandwiches. "Maybe I'm not going to be able to pay my rent."

Patrick Anderson, a consultant and principal at Anderson Economic Group in Lansing, Mich., estimated that the blackout cost Michigan employers about $700 million in net output. About 80 percent of that translates into lost earnings for workers and investors.

Transportation officials in New York said airlines, subways and commuter trains were back on schedule. The sanitation department said it also had resumed normal operations after dealing with overflowing trash cans and mounds of bags filled with spoiled food.

In New Jersey, untreated sewage flowed into Raritan Bay during the power outage, forcing a ban on shellfishing in the bay until unacceptably high coliform bacteria levels fall.