NEW ORLEANS — Much of the city of New Orleans had little to no water pressure for about an hour Sunday, leaving residents with a potential contamination issue.

In a statement late Sunday morning, city officials said a boiler-room power failure at the plant supplying electricity to a water treatment plant caused the drop in pressure. They advised more than 300,000 residents on the Mississippi River’s east bank to boil water for drinking, brushing their teeth or preparing food for at least 24 hours.

Within an hour of the 9 a.m. power failure, tap water was flowing again, and the city said engineers were investigating what caused the failure.

Water will be tested from across the city, the statement said. It takes at least 24 hours to tell whether potentially dangerous bacteria are present.

Most of New Orleans, including the French Quarter and Central Business District, is on the east bank. The treatment plant there provides about 135 million gallons of drinking water a day, compared with 11 million from the west bank treatment plant.

In October, a similar problem occurred at the east bank plant. City officials were criticized because they did not put out a notice that tap water might be contaminated until four hours after the plant shut down. A power problem in November 2010 also created similar conditions.

Across New Orleans on Sunday, some residents and businesses readied water supplies to use under the boil advisory. At Zeus’ Place, a pet boarding and daycare business, owner Michelle Ingram said she was using bottled water for the 80 dogs and 7 cats there.

“We were sitting on 20 gallons of water and I just got 21 more,” she said. “Which should last us through tomorrow afternoon – and hopefully we’ll know then whether or not the boil water order is still on.”

Twitter came alive with residents bemoaning loss of water shortly after 9 a.m. Mayor Mitch Landrieu soon sent this tweet to his followers: “Widespread loss of water pressure reported. We are looking into it the matter.” He later tweeted a link to the boil advisory.

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