Updated: 11 a.m.

A boil water advisory is in effect for the city of Brainerd, Minn., after testing found bacterial contamination in the city water system.

In a statement issued Thursday night, officials said residents on city water should boil it for at least a minute before drinking it, or using it to prepare food or brush their teeth. Residents can also use bottled water as an alternative.

Brainerd Public Utilities officials initially said the affected area is north of Graydon Avenue and Wright Street, to the northern city limits. In an update on Friday, the utility said the advisory was for the entire city.

The city said it is chlorinating the water system.

“Following that time, Brainerd will then flush the chlorinated water and collect samples to confirm there is no total coliform bacteria,” the city reported late Thursday. “We will let you know when tests show the water is safe to drink and you no longer need to boil your water.”

The boil water advisory could last through the weekend, the city reported.

The cause of the contamination hasn’t yet been determined, but the city said it may stem from construction that occurred in late July. Authorities did not elaborate further in their initial statement.