King County sewage rates to soar as stronger storms overpower pipes

King County residents might soon see double-digit sewage rate hikes, and climate change could be part of the reason.

County officials on Thursday proposed a 12.75% spike in sewer rates for 2027 after years of more modest increases. The county's Wastewater Treatment Division says this is likely just the beginning of a series of double-digit percent rate escalations as the county looks for ways to pay for $14 billion in infrastructure upgrades over the next decade.

The proposed sewer rate, if approved by the King County Council, would cost the average wastewater treatment ratepayer an additional $8 per month at a time other utility costs are rapidly increasing and affordability concerns are mounting.

King County says the costs are driven largely by projects required to reduce the amount of sewage that enters local rivers, lakes and Puget Sound.

In some Seattle and King County neighborhoods with older infrastructure, wastewater from homes and businesses flows into the same pipes as stormwater. Nearly all of the time, the combined liquid gets sent to wastewater treatment plants. But around once a year, during heavy rainfall, the system gets overloaded. To prevent sewage from backing into homes and businesses, King County has for decades drained that mixture into nearby bodies of water.

Seattle and King County are working on multiple solutions: building storage tunnels that sewage and stormwater can back into instead of overflowing, separating pipes for sewage and rainwater, and increasing treatment plant capacity. All of these are expensive. And the volume of the problem is growing with climate change.

In December, Washington saw record floods as a series of atmospheric rivers pounded the state. Nearly 5 trillion gallons of rain fell within seven days.

Atmospheric rivers could decrease in frequency as a result of climate change but become 25% wider and longer, effectively doubling the amount of rain they deliver when they land, according to a 2018 NASA study.

King County said climate change-fueled weather events are resulting in much larger volumes of stormwater runoff than expected. Because of that, county officials asked to push back its deadline with the state and federal government to reduce the amount of sewage overflow from 2030 to 2037, which a federal judge granted.

Costs are also increasing as the region's population continues to grow, requiring more pipelines and pump stations. And some of the existing infrastructure, built in the 1960s, needs to be replaced.

King County Executive Girmay Zahilay said increased rates were necessary to support both the region's sewage system and the environment.

"The proposed sewer rate will make sure our front-line professionals have the resources they need to protect the water that sustains life in our region," Zahilay said.

Kamuron Gurol, director of the King County Wastewater Treatment Division, said his department was doing everything it could to keep rates as affordable as possible.

"We recognize that higher sewer rates add to the already high cost of living in the Puget Sound region," Gurol said, "and that the greatest impacts are felt by households making lower incomes."

Correction: An earlier version of this story used incorrect pronouns for Kamuron Gurol.

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This story was originally published April 27, 2026 at 6:42 AM.