Concerns over cloudy water — and having enough water for firefighters — led to rare boil water advisory for all of DC, officials say

An unusual boil water advisory for all of D.C. and most of Arlington, Virginia, was lifted Thursday morning — several hours after hundreds of thousands of residents were urged not to drink water from their taps without boiling it first.

At a news conference Thursday, officials with D.C. Water and the U.S. Army Corps of Engineers, which operates the Washington Aqueduct, said the extensive — and brief — boil water advisory was issued late Wednesday night as a precaution after concerns were raised about increased cloudiness in the drinking water, known as turbidity, caused by an unusually large algae bloom in the Potomac River.

At the same time, crews at the Washington Aqueduct, which provides the public water supply for D.C., were faced with another problem — seeking to replenish worryingly low water levels in the water supply that might be needed for potential firefighting over the holiday.

“Our top priority was to ensure that we had firefighting capability, especially … Fourth of July weekend, here in D.C.,” said Col. Estee Pinchasin, commander of the U.S. Army Corps of Engineers Baltimore District, said during the news conference.

In the end, the boil advisory was able to be quickly lifted Thursday because regular testing indicated the treated water never ended up deviating from drinking water standards, Pinchasin said.

The event marked the first time in nearly 30 years that a boil water warning was issued for all of D.C. In 1996, also over the July Fourth holiday, all residents of the District were urged to boil their water, which lasted about a week, according to D.C. Water.

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

The Arlington County government, which issued its own water advisory Thursday, announced it had also been lifted.

What led to boil water advisory?

The increased algae in the Potomac was essentially clogging the filters at the Dalecarlia water treatment facility leading to low water supply, officials said. That led D.C. Water to shift to using the MacMillan treatment facility in Northeast as a backup. However, officials remained concerned about not having enough supply in the reservoir for any potential firefighting needs.

The aqueduct got permission to use additional chemicals — copper sulfate and sodium permanganate — to combat the algae and started an “aggressive” cleaning regimen to clear the filters to allow more water through the system to replenish the reservoir, Pinchasin said.

While that led to more water supply getting through, there were still concerns about the turbidity of the water — meaning it was cloudier than usual. The cloudy water, by itself, wasn’t a health concern. However, that can interfere with the effectiveness of the disinfection and water treatment process, officials said.

Crews continued monitoring the turbidity levels and issued the boil water advisory as a precaution Wednesday night in case the level would have reached too-high levels sometime overnight, Pinchasin said.

“We didn’t want to have to issue that to people that are sleeping at 2 o’clock in the morning. They’re going to wake up and maybe not check,” Pinchasin said, adding “We wanted to make sure that we were doing the absolute right thing.”

As it happened, the water never fell out of compliance with Environmental Protection Agency standards, she said, meaning D.C. Water could quickly rescind the boil water advisory Thursday morning.

“All our levels are now back up within normal ranges and the treatment and production of water is going very well,” Pinchasin said.

More typically, boil water advisories are sent out after some mishap, such as a loss in water pressure pushes the water out of compliance, which then must be tested multiple times before it is safe to use.

In addition, crews determined that the algae bloom at issue was a green algae that poses no threat to public health, Pinchasin said.

Algae blooms, which are growths of algae on top of the water surface, generally occur when the water gets warmer and are often seasonal in nature. However, the algae bloom that caused the problems Wednesday was particularly large.

“Talking to our teammates that have been here at the aqueduct and serving in the utility world for 45 and 40 years, they’ve never seen anything this large before,” Pinchasin told reporters.

The Washington Aqueduct collects, purifies and pumps about 150 million gallons of water each day.

WTOP’s Neal Augenstein contributed to this report. 

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Jack Moore

Jack Moore joined as a digital writer/editor in July 2016. Previous to his current role, he covered federal government management and technology as the news editor at, part of Government Executive Media Group.

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