Rare tour of Bull Run watershed inspires people who want to know more about Portland's drinking water

Portland's drinking water comes mostly from two reservoirs in the Bull Run watershed near Mount Hood, tapping streams that run through more than 100-square-miles of thick forest. The city also ships Bull Run water to suburbs from Gresham to Beaverton. The gauge measures water levels. Jamie Francis | The Oregonian/OregonLive

Portland water customers will once again drink and bathe in the city's famed Bull Run water starting Wednesday after detections of parasites have gone down.

The Portland Water Bureau said Tuesday it will switch back to delivering customers water from the near-pristine Bull Run Watershed on Wednesday after serving only groundwater for about a month.

The office switched to serving 100 percent groundwater from the Columbia South Shore Well Field following about nine tests from early January to early March that found cryptosporidium in Bull Run water.

The rarity of cryptosporidium findings in the last month offers the city reprieve from the specter that it would have to build an $89 million treatment plant.

Bureau officials wrote in a statement that they expect to continue to find isolated instances of cryptosporidium, but that the public health risk remains low.

"While it is likely that low-level detections of cryptosporidium from the Bull Run will continue, current evidence from public health data, monitoring results, and watershed investigations, as well as extensive consultation with public health officials, have provided confidence in the Portland Water Bureau's decision to resume delivering Bull Run water," the statement said.

The bureau last detected cryptosporidium March 8, after finding the parasite in nine samples this year. The utility office increased its weekly testing of drinking water on Jan 8. after it detected the parasite for the first time in five years. It found the microorganism five times within five weeks.

Unlike most cities, Portland doesn't treat its water for cryptosporidium. Instead, the water flows 26 miles from a 102-square-mile watershed that is off limits to humans and is subject to no filtration and little chemical treatment. The water bureau received an exemption to chemical treatment against cryptosporidium in 2012 from the Oregon Health Authority after it found zero particles of the parasite between 2002 and 2012. The exemption required the city to instead monitor for the parasite regularly.

Finding more than one cryptosporidium oocyst--a microscopic structure found in feces--per 13,300 liters of water in one year would cause the state to revoke Portland's exemption.

The water bureau will continue increased testing until next January.

Water and health officials said the public health risk remains low. Multnomah County Health officials told local clinicians on Feb. 1 to test for expected cases of cryptosporidium infection. Public health officials have reported fewer than expected cases of illness from the parasite in 2017, according to a report from the water bureau.

"Our top priority is to protect public health," Water Bureau Administrator Mike Stuhr said in a statement. "The evidence and data collected, along with input from our partners with the Multnomah County Health Department and regulators at the Oregon Health Authority, indicates the risk remains low."

Still, county health officials urged people with compromised immune systems to consult their physicians.

--Jessica Floum

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