Large algae blooms and concerns about cloudy water prompted rare boil advisory for all of DC, officials say

Boil water advisories in Washington DC and Arlington County, Virginia have been lifted after more than nine hours, effectively affecting both jurisdictions.

The boil water advisory for all of Washington, D.C., and most of Arlington County, Virginia, was lifted Thursday morning, hours after thousands of residents were urged not to drink tap water without boiling it first.

At a news conference Thursday, officials with DC Water and the U.S. Army Corps of Engineers said the boil advisory was issued late Wednesday night as a precaution following concerns about increased cloudiness — known as turbidity — in the water amid an unusually large algae bloom in the Potomac River and the reservoir that serves as its water supply.

However, the advisory was quickly lifted because regular testing showed that the water delivered by the aqueduct never deviated from Environmental Protection Agency standards, said Col. Estee Pinchasin, commander of the U.S. Army Corps of Engineers Baltimore District.

It was the first time in nearly 30 years that a boil water warning was issued for all of Washington, D.C. In 1996, also on the Fourth of July holiday, all residents in the District were urged to boil their water. According to DC Water, that lasted about a week.

In addition to all of Washington, D.C., the nine-hour boil-water advisory also affected nearly all of Arlington County, including the Pentagon, Arlington National Cemetery and Reagan National Airport.

Arlington County authorities, which issued their own water advisory on Thursday, announced that it has also been lifted.

The precautionary advice to boil water began around 9 p.m. on Wednesday

The U.S. Army Corps of Engineers, which manages the aqueduct, said in a statement that it had notified DC Water about problems with increased turbidity in the water supply, which was caused by increased algae blooms in the Potomac River.

DC Water spokesman John Lisle told WTOP the advisory was issued as a precaution to give firefighters access to water, especially on a major holiday like the Fourth of July, and to ensure enough water could be flushed from the system.

“Turbidity can be an indicator of (poor) water quality, and so it was decided that it was safest to issue the boil advisory,” Lisle said.

While the cloudy water itself has no health effects, it can disrupt disinfection measures and make it easier for microbes to multiply, DC Water said.

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