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9611 SE 36th Street
Mercer Island, WA 98040
Phone: 206.275.7783
Fax: 206.275.7787
Email: mifinance@mercergo. . .
Hours: 8:30 am - 5:00 pm (Mon - Fri)
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City of Mercer Island / Finance / Utility Services

Utility Services

Residents, businesses, and multi-family units are billed on a bi-monthly basis for drinking water, sewer, storm and surface water, and emergency medical services.  The following services and information are provided by the Utility Billing Department:

If you have questions call the Utility Billing Department Customer Service Representatives at 206.275.7783.

Drinking Water

Water charges are based on the size of your meter and the amount of water you use. The meter charge and water consumption charge are shown separately on your utility bill. The meter charge is a fixed amount based on the size of your water meter and supports services such as meter repairs, meter reading, and customer service.  Water use, or consumption, is the amount of actual water used.  Consumption is measured by a bi-monthly meter reading and is billed in units of 100 cubic feet (ccf). One cubic foot of water is equal to about 7.5 gallons. While residential rates increase with higher use, commercial rates are determined by season and are higher in summer peak months Single family customers also pay a conservation surcharge for bi-monthly use above 20 ccf in the four summer months of June through September.  The Conservation surcharge is designed to encourage responsible water use and supports on ongoing conservation program.


Sewer charges for customers are a combination of a sewer treatment charge set by King County Wastewater Treatment and a local rate based on water use volume.

The City of Mercer Island contracts with King County Wastewater Treatment for the transportation and treatment of sewage waste.   The cost for this service is passed through to the utility customer.  For single family customers, the King County rate is a fixed amount.

The local portion of the sewer bill is based on the customers average water use during the previous winter months of December through March, or January through April depending on the billing cycle.  Multi-family and Commercial customers pay both the King County Sewage Treatment  and local rate based on their actual water consumption.

Storm and Surface Water

Storm and surface water fees cover the costs associated with controlling surface water runoff, maintaining and improving the public drainage system, and protecting water quality in Lake Washington.  Storm water service charges are based on the size of your property and the percentage of impervious surface on that property. Impervious surfaces, such as roofs, driveways and decks, are those which don't absorb water and therefore contribute to storm water runoff. All single-family residences pay a rate based on an average of 3,471 square feet of impervious surface per property. The rate for all other property (commercial, multi-family, etc.) is based on the actual measured impervious surface, with 3,471 square feet considered to be 1 equivalent service unit.

Emergency Medical Services

Utility customers pay a small fee to help provide for the emergency medical services provided by the Mercer Island firefighters. City firefighters, who are all trained as emergency medical technicians, are notified first in case of a 911 call. They respond in specially equipped aid cars to provide immediate life support assistance.

Paying Your Utility Bill

There are multiple options for remitting payment for your Mercer Island utility bill. If you have questions regarding your bill contact the Utility Billing Team at 206.275.7783, Monday through Friday, 8:00 am to 5:00 pm.

  1. Pay your utility bill online using Visa, MasterCard, Discover, or by electronic check from your bank account (checking or savings). You can also elect to receive paperless bills via e-mail.  For instruction about using the City of Mercer Island’s online bill presentment and payment site, please see Instructions.  If you have detailed questions, please see Frequently Asked Questions (FAQ’s).
  2. Pay your bill in person at Mercer Island City Hall (9611 SE 36th Street, Mercer Island, WA  98040).
  3. Pay your utility bill by mail by sending a check or money order to the address listed above. Please include your account number on the check. 

After Hours Assistance

For reporting problems outside of regular business hours, call the non-emergency police number at 425.577.5656.

Utility Rates

Utility rates are established based on a bi-monthly billing cycle and are adopted by the City Council on an annual basis.  For detailed information regarding emerging issues and capital reinvestment programs, for each of the Mercer Island utilities, see the Utility Fiscal Policies section of the 2019-2020 Budget document.  Current year rates are available here: Bi-Monthly Utility Rates

Utility Bill Adjustments

The City has two policy regarding adjustments to utility bills:

  1. Utility Account Adjustment Policy
  2. Leak Adjustment Policy

Utility Service Discounts

Assistance with City water, sewer line maintenance, and storm water charges is available to low income seniors and disabled persons.  Additionally, assistance is available with charges for Emergency Medical Services for Medicaid eligible persons receiving in-home care.  For more information on eligibility and the application process, see the Utility Service Discount page.


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