WASHINGTON -- About 34,000 residents across a large swath of the northern portion of the District have been issued a precautionary boil water advisory by DC Water early Friday morning.

DC Water put out an updated map just before noon on Friday, which decreased the scope of the advisory. The interactive map is below:

The advisory comes after many D.C. residents experienced low water pressure or a complete lack of water service after 8:30 p.m. Thursday. According to a press release from DC Water, the problem started with an open valve at the Bryant St. pumping station which caused a loss of pressure in portions of the distribution system for approximately one hour. DC Water says the loss of pressure in the pipe system makes it possible for the water to become contaminated, but as of right now there is no confirmation of contamination in the water.

DC Water advises those who lost pressure or service after 8:30 Thursday night to adhere to the boil water advisory. If any customers do not have service, they should boil water after it is restored. Officials are expecting the advisory to last for at least 24 to 48 hours. If you are a DC resident and did not experience any problems Thursday night, you do not have to boil your water.According to DC Water, customers who have discolored water to run the tap until it clears before boiling. Water should be brought to a rolling boil for three minutes and then allowed to cool before using or storing in a clean container with a cover.

The cooled boiled water should be used for drinking, brushing teeth, preparing and cooking food, making ice, preparing infant formula, or giving water to pets.

DC Water said It is safe to take a bath or shower, but be mindful not to swallow any water.

The valve problem has been corrected and normal water service restored. Teams are testing samples and will lift the advisory when they determine the water is safe.

Officials are investigating the cause of the broken valve. None of the water spilled or was lost.

For more information, visit http://www.dcwater.com, or read the FAQs at dcwater.com/boilwaterFAQ. You may also contact DC Water Customer Service at 202.354.3600 or the 24-Hour Command Center at 202.612.3400.