July Fourth cookouts inside the Beltway became a lot more complicated late Wednesday night.

Local water systems issued a boil-water advisory affecting all of the District of Columbia and almost all of neighboring Arlington County because of impurities found in the Washington Aqueduct.

Notices were sent to residents in both jurisdictions via emergency cell-phone notices that began appearing after 11 p.m.

“This is a precautionary notice to all customers to boil water that may be ingested due to water of unknown quality. Customers should not drink the water without boiling it first. This advisory will remain in place until follow-up testing confirms the water is safe to drink,” D.C. Water said in its advisory.

According to Arlington County’s advisory “higher levels of turbidity have been observed in water held at the Aqueduct, which is sourced from the Potomac River” and serves both communities.

“Turbidity” measures visible articles in water and produces a cloudy or hazy appearance. It has no direct health effects itself, but it can hamper the water-treatment process and may also indicate the presence of bacteria.

“The advisory is issued out of an abundance of caution,” Arlington County said.

The U.S. Army Corps of Engineers operates the aqueduct.

Neither jurisdiction gave any indication what might have led to the turbidity and said that customers would be told when the water would be safe to drink again without boiling.

The jurisdictions advised their customers to run cold water, bring it to a rolling boil for at least one minute, and let it cool before use.

Not only should the water not be drunk, but it also should not be used in ways that might lead to ingestion such as washing dishes, cleaning vegetables, or rinsing teeth after brushing. It also should not be given to pets or used to mix baby formula.

Arlington County advised that a sliver of its residents needn’t worry — those in the Willston Pressure Zone, which borders Fairfax County near the intersection of McKinley Road and Wilson Boulevard.

The water systems of several neighboring jurisdictions — Fairfax County and the city of Alexandria in Virginia, and Montgomery and Prince George’s counties in Maryland — all posted on social media late Wednesday night that their water systems were unaffected.

However, Alexandria cautioned that “residents and businesses near Arlington County might receive a text about a boil water advisory. This advisory is for Arlington County and DC only. Alexandria’s water supply is not affected.”

• Victor Morton can be reached at vmorton@washingtontimes.com.