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Starting Monday, the Portland Water Bureau switched to its backup water source, groundwater from wells along the Columbia River.

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The Water Bureau said it has stopped using Bull Run water out of an “abundance of caution” in response to repeated detection of a parasite known as cryptosporidium. It may take up to two weeks, depending on location, for groundwater to make its way through the distribution system to homes and businesses.

In the meantime, the Water Bureau says the Bull Run water remains safe to drink for healthy people, but that people with compromised immune systems should seek advice from their doctors. That includes people undergoing chemotherapy, people on immune suppressing drugs, infants and some elderly people.

The Portland Water Bureau serves more than 1 million people including customers in Portland and several of its suburbs. The city agency has received permission from state and federal regulators not to treat water from the Bull Run watershed for cryptosporidium. The water agency sometimes supplements or replaces Bull Run water for other reasons, such as during the summer dry season or when heavy rains cause high sediment levels in the Bull Run.

OPB asked Portland Water Bureau director Mike Stuhr to explain the decision to temporarily switch to groundwater. Here are the highlights:

What has caused this occurrence of cryptosporidium?

You know that old adage about bears in the woods? A common source for cryptosporidium is animal feces. Stuhr’s theory: Heavy rainfall this winter has led to even more animal waste than usual being flushed into the Bull Run’s two lakes.

“We have a highly protected watershed. It’s arguably one of the most protected in the country. But there are a lot of wildlife up there,” he said.

State regulators with the Oregon Health Authority did not require the city to make this switch.

“No, we made this on our own,” Stuhr said. “We typically turn groundwater on and off for a variety of reasons throughout the year and for us this was a normal operational thing.

So why switch now?

“You’ve been reporting for the last few weeks, this dribble of crypto oocysts that have been showing up. It’s continued. We just decided at this point we wanted to study it a little bit more, and we have this wonderful secondary source that’s ours to use,” Stuhr said. “We thought it would be in the best interest of all if we switched to using the groundwater system. We’re going to continue to monitor the water up in Bull Run lakes and study it some more.”

How long will the switch to groundwater last?

The short version: City leaders don’t know.

“We’re going to continue to sample Bull Run for crypto. When we have enough additional information about the source and the cause of these detections, we’ll talk again with OHA and the county, our public health partners, and we’ll make a determination,” Stuhr said.

City leaders say the water coming through your taps is safe.

“Absolutely,” Stuhr said. “We’re not required to do this. We’re just a very cautious agency. We take great care and great pride in the water we serve. We want to make sure we’re doing the best we can. ...

"Our health partners — OHA and the county health department — say that our water is perfectly safe to drink, and it’s within limits.”

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