More than 600,000 residents in Portland, Oregon are being told by the state to boil their drinking water following the discovery of E. coli bacteria in some water samples being tested.
An advisory about boiling drinking water was issued by the city's Water Bureau and a number of other local water districts to a total of around 670,000 customers, who were urged to boil tap water intended for drinking, cooking, brushing teeth or making ice for a full minute at a rolling boil.
Officials also urged they discard any ice or beverages prepared after May 20.
"While we believe at this time that the potential health risk is relatively small, we take any contamination seriously and are taking every precaution to protect public health," Portland Water Bureau Administrator David Shaff said in a statement.
Three water samples tested from May 20 to May 23 "confirmed the presence of total coliform and E. coli in routine drinking water samples," the bureau said.
While most forms of E. coli are either harmless or just bring on a brief bout of diarrhea, some more virulent strains can lead to bloody diarrhea, abdominal cramps and vomiting.
E. coli contamination is the result of animal or human fecal material, and officials said there were exploring how it was introduced into the area water supply. Animal waste was the more likely source, they said.
Anything that exposes drinking water to the elements, such as loss of water pressure or broken pipes, can lead to contamination, they said.
Two reservoirs have been taken out of use by the bureau while additional sampling is being carried out in the suspected affected area.
Portland-area residents have seen such boil water alerts before, one in 2012 affecting 135,000 households and a smaller one in 2007 covering 50,000 residents.
Both of those alerts were also the result of E. coli contamination.
One local business was taking the alert in stride.
"We're not using ice, we're not using anything that's not hot," said Rebekah Yli-Luoma, co-owner of Portland's Heart coffee shop. "But we're also informing the customers about what the situation is. And if they want to drink at their own risk, they can."