Portland officials issued a citywide boil notice after state health officials detected E. coli in the water supply.
The Portland Water Bureau said residents should boil all tap water used for drinking, food preparation, tooth brushing and ice for at least one minute.
Ice or any beverages prepared with unboiled tap water on or after Tuesday should be dumped.
The water samples that tested positive for bacteria were collected from two reservoirs at Mount Tabor.
Tri-County Health Officer Dr. Paul Lewis says the E. coli is unlikely to cause any health problems, except for maybe diarrhea.
The Water Bureau is investigating the cause of the contamination.
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