OXON HILL, Md. » Hundreds of thousands of people in suburban Washington are sweating through a punishing heat wave under orders to avoid long showers, turn off sprinklers and think twice about flushing the toilet.

Carwashes, day care centers and fast-food restaurants shut their doors today. And the military base that is home to the president’s Air Force One was reduced to essential operations.

The reason for the restrictions: urgent repairs to a nearly 50-year-old water main in Prince George’s County that authorities said was in danger of failing.

More than 200,000 residents and businesses in the county are under mandatory water restrictions, possibly for days, while the mercury is expected to climb into the 90s.

The warning to the public came late Monday night, giving people about 24 hours to stock up on bottled water and prepare for days without washing clothes or dishes.

Still, things could have been worse. Officials initially warned that faucets could run dry for several days during the repairs.

But today, officials said they were able to divert enough water to keep it flowing. They said the water main should be back in service in two or three days if nothing unexpected happens.

"If we continue to conserve we’re confident that the system will remain full while we complete the repairs on the pipe and return it to service," said Jerry N. Johnson, general manager of the Washington Suburban Sanitary Commission.

The repairs were ordered after a monitoring system inside the 4½-foot-diameter water main started sending warnings late last week that the concrete pipe, installed around 1965, was in trouble.

Residents were told to postpone using dishwashers and washing machines, to limit the flushing of toilets and to take short showers.

Joint Base Andrews, which is home to Air Force One and has 16,000 residents and workers, shut down all but the most critical operations. A base clinic was accepting only emergency patients.

At a kidney dialysis center in Oxon Hill, a tanker truck pumped water into the clinic, which uses 5,000 gallons a day. And a Shoppers Food Warehouse just off the Capital Beltway in Oxon Hill was restocking the shelves with hundreds of jugs of water after customers bought them all.

Residents were delighted the crisis wasn’t as bad as they feared.

"Thank the Lord!" said Tina Wiseman, a cashier, after learning that her water would not be shut off.

"I can’t live without water for five days. I’m clean. I take a lot of showers," she said.

John Smith, a bus driver who lives in Temple Hills, had two 24-packs of bottled water in his shopping cart when he found out his water would not be shut off. He said he planned to buy them anyway, but grumbled: "Fine time to tell everybody."

"I just went home and filled my bathtubs up. I’ve got eight other buckets around the house," he said.

Tony Hall of Washington was surprised by the effects of the water crisis.

"I went to McDonald’s, and they were closed. It takes a lot to close down a McDonald’s," he said. "If a McDonald’s closes, the world is about to come to an end."

Gresko reported from Washington. Associated Press reporters Sarah Brumfield and in Washington and Brian Witte in Annapolis contributed to this report.