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In King County’s wastewater service area, owners of buildings with new sewer connections, additions or changes of use pay their share of the cost of sewer infrastructure through a capacity charge. Two studies began in 2017 to look at the affordability and rate design of the capacity charge.

November 2020

The King County Council has approved updates to the capacity charge rate structure and will use average persons per household as the new basis of the capacity charge effective Jan. 1, 2021

For the latest update on the capacity charge rate study, read our Fall 2020 Update .

Capacity charge rate study

The King County Council has approved updates to the rate structure of the capacity charge. Effective Jan. 1, 2021, the County will use average persons per household as the new basis of the capacity charge for residential structures. 

This change to the capacity charge residential rate structure will tie the amount that people pay to the average number of people per household by housing type, which is based on data from the U.S. Census Bureau.

For single family homes, the updates mean that small homes will pay less for the capacity charge and large homes will pay more beginning in 2021. The Residential Customer Equivalent (RCE) assigned to single family homes would be based on size: small (<1,500 sq. ft. = 0.81 RCE), medium (1,500 – 2,999 sq. ft. = 1 RCE), and large (>3,000 sq. ft. = 1.16 RCE). 

Using persons per household data will also result in small changes to RCEs assigned to multi-family units. These changes will also confirm a previous interim change for accessory dwelling units, like backyard cottages and basement apartments, and set a 0.59 RCE for those units.
The approved changes are designed to be revenue neutral so that it does not increase the overall amount that King County collects through the capacity charge.

Why the update?

The purpose of updating the rate structure is to respond to changing housing trends by making the capacity charge better reflect the amount of wastewater a home is likely to send to the sewer. Using average persons per household allows King County to update the basis for the capacity charge as demographics change.

Since the capacity charge program began in 1990, King County has experienced significant growth and change. Emerging trends include micro-housing, small efficiency dwelling units, accessory dwelling units, detached accessory dwelling units, group housing, adult care homes, and the installation of low-flow plumbing fixtures. 

The rate design study was designed to evaluate the best approach for allocating the capacity charge in light of the wastewater demand for today’s building types. 

Low income customer assistance

King County Wastewater Treatment Division recently implemented new affordability options for capacity charge customers based on the findings of a Low-Income Customer Affordability Study . The new assistance programs approved by the King County Council and signed by the Executive took effect June 29, 2019. Assistance aimed at customers experiencing financial hardship include:

  • Payment deferral for low-income seniors and disabled individuals: Customers who enroll in the State and County property tax exemption program for seniors and disabled individuals may be eligible to wait until they sell their property to pay the capacity charge.  King County will place a property lien for the balance owed and collect the funds when the property is sold. The interest rate is reduced to 5 percent annually and late fees are waived, however a recording fee will apply.
  • Improved payment plan options: Payment plans for the capacity charge can be more flexible. They allow customers to catch up on late bills through smaller, more frequent payment plans. 
  • Connecting customers to resources: Staff can refer customers to Washington 211, which provides referrals to a variety of health and human services.
  • Affordability for new low income housing: More types of eligible low-income housing can qualify for a discounted capacity charge. Eligible new units will be assigned 0.32 residential customer equivalents, which in most cases represents a 50 percent discount. See this table for details on qualifications by housing type.

Next steps

The Low-Income Customer Affordability Study is completed and new assistance programs approved by the King County Council and signed by the Executive took effect June 29, 2019. The Rate Design Review Study is completed and the updated rate structure will take effect on Jan. 1, 2021. The County is working with local sewer districts and will provide updated forms to record the size of single family homes that connect to the sewer system on or after Jan. 1, 2021, and assign an RCE category.

Contact Us

Phone: 206-296-1450

Fax: 206-263-6073