The D.C. Water and Sewer Authority warned some District residents Friday to boil their tap water before cooking or drinking “until further notice.”

The advisory was sent to District residents Friday at about 4:30 a.m. and affects parts of Northwest and Northeast D.C. The water department initially issued a map showing that the southern boundary of the affected area crossed through Washington Circle near GW Hospital, but an updated interactive map places the border at 23rd and P streets NW.

Officials said water may have been contaminated after an open valve at a Northwest pumping station resulted in a pressure loss Thursday night. The valve issue was fixed and water pressure is back to normal in affected areas, according to the advisory notice.

The boil-water order is expected to last 24 to 48 hours, D.C. Water announced on Twitter Friday morning. The department said there are no confirmed cases of drinking water contamination.