King County Proposes 12.75% Sewer Rate Increase For 2027

King County officials are proposing a 12.75% increase in sewer rates for 2027, a move that would raise monthly costs for the average ratepayer by about $8 as the region faces mounting infrastructure and regulatory demands.

The proposal, transmitted to the King County Council, is intended to fund upgrades to an aging wastewater system, meet state and federal environmental regulations and expand capacity to serve a growing population.

County Executive Girmay Zahilay said the increase is necessary to maintain water quality and protect public health.

“The proposed sewer rate will make sure our frontline professionals have the resources they need to protect the water that sustains life in our region,” Zahilay said. “We have an obligation to the people we serve to be just as effective at financial stewardship as we are at environmental stewardship.”

King County’s Wastewater Treatment Division serves nearly 2 million people across King, Snohomish and Pierce counties, along with the Muckleshoot Indian Tribe. The system processes an estimated 178 million gallons of wastewater each day through a network of treatment plants, pump stations and nearly 400 miles of major sewer lines.

Much of that infrastructure was built decades ago and is now approaching the end of its service life. Officials say daily wear and tear, combined with the corrosive nature of wastewater, has pushed some equipment to the point where replacement parts are no longer available, increasing the urgency for upgrades.

A current example of that work is the M Street Trunk Rehabilitation Project in Auburn, which will repair about 2.6 miles of deteriorating sewer pipe as part of broader efforts to modernize the system.

Over the next decade, the Wastewater Treatment Division estimates it will need about $14 billion to upgrade infrastructure, comply with regulations and expand the system to accommodate future growth. About half of those costs — roughly $7 billion — are tied to state and federal regulatory requirements.

Those requirements include reducing combined sewer overflows, which occur when heavy rainfall overwhelms pipes that carry both stormwater and sewage. While the county has reduced these events in recent years, a federal consent decree requires further reductions by 2037.

The county must also meet conditions tied to a federal discharge permit for the West Point Treatment Plant in Seattle and contribute to cleanup efforts at the Lower Duwamish Waterway Superfund site.

Officials say population growth is another major factor driving costs, as more homes and businesses connect to the regional sewer system, requiring additional pipeline capacity, expanded treatment facilities and a larger workforce.

The proposed increase marks the beginning of what officials describe as a period of higher rate hikes, following years of more gradual increases tied to rising operational costs such as electricity and chemicals.

County leaders acknowledged the impact higher rates could have on residents, particularly those already facing rising housing and utility costs.

“We recognize that higher sewer rates add to the already high cost of living in the Puget Sound region, and that the greatest impacts are felt by households making lower incomes,” said Kamuron Gurol, director of the county’s Wastewater Treatment Division.

In addition to the rate increase, the county is proposing a 6.55% increase in the capacity charge, which applies to new users connecting to the system and helps fund future infrastructure expansion.

To address affordability concerns, officials say they are pursuing several strategies, including seeking low-interest loans from state and federal programs, improving cost controls and working with regional partners to increase transparency and predictability in long-term planning.

The Wastewater Treatment Division has historically maintained strong credit ratings, allowing it to secure favorable financing and reduce borrowing costs for ratepayers. Over the past decade, officials say the county has saved more than $160 million through low-interest loan programs.

The proposal will now move to the King County Council for review as part of the rate-setting process.