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

The Portland Water Bureau has temporarily stopped delivering Bull Run water to Portland water users after finding the cryptosporidium parasite six times in tests of drinking water from the Bull Run watershed since Jan. 1.

The bureau will instead deliver 100 percent groundwater from the Columbia South Shore Well Field, a decision city officials said is "not required." It could take as many as two weeks for the groundwater to make its way to homes and businesses.

Water officials said they decided to switch water sources "out of an abundance of caution." They don't know when the bureau will start delivering Bull Run drinking water again or what conditions would make them comfortable doing so, Water Bureau director Michael Stuhr said. Stuhr said they will continue monitoring the Bull Run water and will test whether the cryptosporidium found is harmful to humans.

"The recent detections do not pose an increased health risk," Stuhr said in a statement. "After a series of very low level detections, we are proactively activating our secondary source while we collect more data."

The Portland water bureau has detected the cryptosporidium pathogen in drinking water from Bull Run at least six times this year, raising the risk that the city could have to build a treatment plant that could cost tens of millions of dollars.

The bureau increased its weekly testing of drinking water on Jan. 8 after it detected the parasite for the first time in five years. The bureau detected the microorganism five more times within the next five weeks. Water officials noted that this many positive tests in such a short window was the most they'd seen in more than a decade. They will continue increased monitoring for one year.

Multnomah County Health Officer Paul Lewis said in an interview that it's unlikely the cryptosporidium found is harmful to humans because it likely originates from the scat of animals living near Bull Run. Humans are prohibited from accessing the protected watershed, and animal-borne pathogens do not often affect humans, he said.

Still, people with compromised immune systems should talk to their doctors about alternative drinking water options, Lewis said.

"This is a cautious approach," Lewis said. "We don't really know if anyone is going to have a problem with cryptosporidium."

Unlike most cities, Portland does not treat its water for cryptosporidium. The Oregon Health Authority gave the city an exemption in 2012 from federal treatment rules, allowing the city to instead monitor for the parasite through regular testing.

The state could revoke Portland's exemption, called a variance, if the water bureau finds more than one oocyst - a hard, microscopic structure found in feces - per 13,300 liters of water in one year. This could force the bureau to build an ultraviolet treatment plant, expected to cost at least $89 million, according to water bureau planning documents, or a filtration system that could cost around $300 million.

Stuhr said in a statement that the water bureau is still in compliance with the variance.

Switching to delivering only groundwater could prove costly to the bureau. The water bureau often supplements its Bull Run drinking water with groundwater. Drawing on both sources is more economical, bureau spokeswoman Jaymee Cuti wrote in an email. The pump system required to deliver groundwater is more expensive than using gravity to draw water from Bull Run.

Update: This story has been updated to reflect when the water bureau increased its monitoring for cryptosporidium. Water officials increased their testing Jan. 8.

--Jessica Floum

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