Portland has just six weeks to decide how it will comply with a state order to protect its drinking water from parasites while keeping bills down for ratepayers.

By August, the City Council must choose between spending up to $500 million and 12 years to build a filtration treatment system or about $105 million and five years on a facility that will treat water with ultraviolet light.

The council considered a combination of the two options in a work session Tuesday.

Portland's drinking water comes from the Bull Run watershed and travels to Portland area homes with almost no treatment. In 2006, federal rules required that cities with unfiltered water systems treat for cryptosporidium.

The Oregon Health Authority, however, permitted Portland an exemption, so long as the bureau regularly tested for cryptosporidium and found none.

That worked well for water drinkers and rate payers for years. But the discovery of 19 cryptosporidium parasite structures in 14 water samples from January through March means the city now must build a treatment plant, as ordered by the state health authority on May 19 .

"This winter and spring, we got a fairly big surprise," Water Bureau director Mike Stuhr said Tuesday.

Although the unusual rate of cryptosporidium findings surprised the bureau, considering potential treatment options is no new task. Stuhr said he experienced déjà vu Tuesday, since he presented the council with the same treatment options in 2009, after which the city council decided to seek a state exemption instead.

The bureau spent $16 million and several years developing a design for an ultraviolet treatment plant that got shelved in 2012, he said. The council now has no choice but to choose a treatment option by August, he said.

"Water professionals try to be ahead of the game for regulation when we can because being up against these type of deadlines is difficult, to say the least," Stuhr said.

To get ahead of an increasingly restrictive regulatory environment, Stuhr said he would opt for a treatment plant that uses sand or charcoal to filter dangerous pathogens, sediment and other contaminants. It could also increase the supply of useable water, which Stuhr said is important considering climate change is expected to create dryer, hotter summers and higher water demand.

"If I was made of money, I would build a filtration plant and I wouldn't think twice about it," Stuhr said. "It does so many things."

But Stuhr isn't made of money and doesn't have much time to comply with the state order, he said. The filtration plant could cost up to $400 million more than an ultraviolet treatment plant and take at least twice as long to set up.

However, an ultraviolet plant would not address future regulations, doesn't get rid of sediment and does nothing to increase supply, he said.

"Obviously there is a cost-benefit trade off here," Mayor Ted Wheeler said Tuesday.

The mayor asked if it's possible to build the UV plant in the short term to bring the city into federal compliance and then pursue a filtration plant later.

"Can we make the investments we're making today go toward the plans for tomorrow?" Wheeler asked. "Or is that a pipe dream?"

Water Commissioner Nick Fish and Stuhr agreed that pursuing UV treatment in the short-term and filtration in the long-term could be the best option to achieve compliance while keeping water bills down for ratepayers. That would give the city time to set aside money to build a filtration plant later, Stuhr said.

Fish encouraged members of the public to share their thoughts at a July 11 Public Utility Board meeting, at which the board will come up with a recommendation for the council.

Janice Thompson, advocacy director for Oregon Citizens' Utility Board, encouraged the council to consider the risks of going with the cheaper option.

"Sometimes the thing that's the cheapest doesn't end up being the cheapest when you factor in risks involved," Thompson said.

So far, public health officials report that there were fewer cases of illnesses caused by cryptosporidium this year than average. There are multiple forms of cryptosporidium, only some of which make people sick, and the animal droppings believed to have led to the tainted samples this year don't contain the type harmful to people.

--Jessica Floum

503-221-8306