PORTLAND -- The Portland Water Bureau issued a 'boil water notice' Saturday for customers west of the Willamette River. People in the affected area should not drink tap water without boiling it first.
Customers are also affected in the Burlington Water District, Valley View Water District, Palatine Hills Water District, City of Tigard, Lake Grove Water District and West Slope Water District, according to Tim Hall of the Portland Water Bureau. He said customers of the Tualatin Valley Water District would not be affected.
"All tap water within the defined area used for drinking, food preparation, and ice should be boiled at a full rolling boil for at least one minute," he added. "Ice or any beverages prepared with tap water after Thursday should be discarded."
Portland Mayor Sam Adams also warned people not to drink from west side public drinking fountains.
A sample collected Thursday from reservoir 3 in Washington Park showed possible bacterial contamination. The reservoir was shut off and additional samples were collected.
The bureau announced in a statement Saturday morning that one of the follow-up samples tested positive for bacteria, "the presence of which indicates that the water may be contaminated with human or animal wastes."
"Although these bacteria are generally not harmful, their presence in drinking water could indicate harmful organisms might have entered the distribution system, so we are taking every precaution to protect our customers," bureau administrator David Shaff said.
Microbes in contaminated waters can cause diarrhea, cramps, nausea, headaches and other symptoms, especially in infants, young children and people with compromised immune systems.
The specific strain of E. coli was unknown, according to the Saturday statement, which added that the strains generally linked to serious illness are rarely found in water supplies.
The water bureau will announce when samples no longer contain bacteria and boiling water is no longer necessary. The next test results were expected Sunday morning.
View Boil Water Notice -- Portland Water Bureau 7-21-2012 in a larger map