The humble ultraviolet wave, it seems, never had much of a chance.

From the first moments of a lengthy hearing Wednesday afternoon on what type of federally mandated water treatment Portland would choose, the cheapest option—a $105 million plant that would use UV rays to eliminate a parasite found rarely in Portland's water—was painted as inadequate.

Instead, the big-ticket option won out: A 30-acre filtration plant that's estimated to cost between $350 and $500 million. After a series of invited guests unfolded as an infomercial for a filtration plant, council voted unanimously to move forward, the first step in a lengthy process that will see Portlanders' water rates rise to pay for the facility.

The decision is a weighty and fairly abrupt about-face for a city that's long preened in its relatively pristine water supply. And it came even though officials had extra time to think things through. The Oregon Health Authority, which in May gave notice that Portland would need to treat its water supply for the parasite cryptosporidium, offered a 60 day extension to a September 11 decision deadline late yesterday.

But it didn't matter.

A litany of testimony persuaded commissioners—along with the Multnomah County public health officer, and two bodies that scrutinize water rates—that filtration was the best option.

"It sounds like thus far people have made a much stronger case for a filtration strategy," Mayor Ted Wheeler said early on in the hearing. Nothing much changed from there.

The decision was rooted, oddly, in the fact that Portland doesn't currently have a problem with its water.

Since 2012, the city has had the lone water system in America not required under federal rule to treat for cryptosporidium, a parasite that lives in human and animal waste and in some forms can cause sickness. The "variance" to the rule was granted for a simple reason: Portland's Bull Run watershed doesn't carry much crypto.

But during this winter's intense rains, that changed. From January to March, officials believe those rains washed more animal waste—and therefore crypto—into the watershed. The city turned up 19 instances of the parasite, and the Oregon Health Authority has said Portland now has to treat its water.

The city hasn't detected cryptosporidium since March, and Public Health Officer Paul Lewis told commissioners today there's no proof that the type of crypto Portland found was even a risk to human health (plenty of detractors make the same point).

"Enough time has now gone by since the winter months when there were frequent detections… to know there were actually slightly fewer cases reported during that time period," Lewis said.

But the city's locked by the state into additional water treatment. The question city council took up today was what kind.

A UV plant would address crypto, and nothing else. The filtration plant, officials told council, would address a litany of issues that might pop up in coming decades—things like forest fires that could damage water quality, and additional government regulation. There was also a "hybrid" plan that would have seen Portland building a UV plant in the near future and socking away cash to perhaps build a filtration plant down the line.

By the time council took up the matter, only those last two options seemed to have support, and they were the only proposals that the water bureau analyzed in terms of water rate increases in coming years.

And the bureau saved its most robust arguments for filtration. While moving forward with a more expensive project means higher costs in the near term, officials submitted an analysis that suggested the plant would offer enough positives—fewer worries about summer algae and sediment, higher water quality, and more—to equate to a roughly $5.4 million benefit per year.

The bureau also suggested that, given risks to the water system and potential new federal regulations, there's a 50/50 chance Portland will have to build a filtration plant anyway in 27 years—and a more than 70 percent chance by nearly 50 years out.

And as Lewis noted, there is no sign cryptosporidium is a problem, so why pick a UV option?

"Our [water system] is pretty special, and as far as we can tell the risk is very low," Lewis said. "We should’t rush to do UV, which is really just a one-trick pony."

Plenty of people pushed back.

Floy Jones, a member of the group Friends of the Reservoirs who tirelessly advocates against changes to the water system, argued against any treatment, saying there's no evidence of a health problem.

"The goal [of federal rules] is to reduce the level of disease in the community," Jones said. "We don't have disease in the community." She told commissioners there was no sign additional federal regulations are on the horizon, and called the water bureau's probability and cost analyses "rushed."

Others wanted council to slow down.

"Our chief concern is that decisions with long-term impacts… are being made in a rush based on fear without adequate scientific consideration of the alternatives," said Theodora Tsongas, of the group Oregon Physicians for Social Responsibility. Adding to water rates "with no public health purpose or benefit," she said, would only exacerbate the city's skyrocketing cost of living.

Tsongas and other testifiers urged the city to push for a delay on a decision until next June.

They found one commissioner who was open to at least some delay. Commissioner Amanda Fritz was the lone council member who voiced misgivings about making a decision Wednesday.

"This is a huge amount of public money," said Fritz. "And you did go and get those 60 days."

But the writing, at that point, was on the wall. Wheeler and city commissioners Nick Fish, Dan Saltzman, and Chloe Eudaly were all happy to move forward with a filtration plant.

"I think we need to think 100 years and not 20 years forward," said Fish, indicating his preference for filtration.

Wheeler called a filtration plant "the only reasonable option left on the table."

Eudaly said: "I don't relish the though of the taste or any quality of our water changing. I would prefer not to do filtration. The fact is that we have lost our variance."

And Fritz didn't hold out. After being assured that the city would address the questions of two oversight bodies, the Portland Utility Board and the Oregon Citizens' Utility Board, she indicated she'd vote for filtration.

"You have won my trust," Fritz told Fish, the commissioner who oversees the water bureau. "I'll be willing to support your resolution."

"That means the world to me," he replied.

The city now needs to provide a schedule for coming into compliance with federal rules by late November. There's much still in the air about precisely what kind of plant ratepayers will pay for.