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9601 SE 36th Street
Mercer Island, WA 98040
Phone: 206.275.7608
Fax: 206.275.7814
Email: publicworks@mercer. . .
Hours: 7:30 AM - 4:00 PM (Mon-Fri)
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Water Utility

Water Reservoir
Water is delivered to Mercer Island by Seattle Public Utilities via 16" and 24" water supply lines.  The water is stored in two 4-million gallon reservoirs for domestic use and fire protection.  Water is distributed through 4" to 30" waterlines and is delivered to customers through approximately 7,800 water meters.  Water quality testing and monitoring is performed as required by the Environmental Protection Agency Safe Water Drinking Act. 

Cross-Connections & Backflow Prevention Devices
Click here for more information.

Water Utility Billing
Visit the Water Utility Services page here.


Watersheds: The Source of Our Water
The regionís fresh water supply water comes primarily from two sources: the Cedar River Watershed and the Tolt River Watershed, both located in eastern King County. The watersheds are large, uninhabited land areas that gather and store rain and snowmelt. Year-round, 26 cities and water districts rely on a limited supply of stored water from these two sources to meet most of the daily needs of business, government, institutions and 1.3 million people in our region. In addition to providing clean, clear, reliable drinking water, the watersheds also provide habitat for fish and wildlife.

Water Conservation Tips: How to be Waterwise
Water conservation is important for our region, our environment, future generations and your pocketbook.  Click here to visit our conservation pages and learn how to be waterwise.

Just how much water does Mercer Island use anyway?
Historically, Mercer Island has been one of our region's biggest water users during the summer "demand" season. A variety of conservation efforts funded through the Water Utility are targeting this seasonal peak in consumption. Click here to see how much water the Island uses each month.

Water Quality Report
The City of Mercer Island is pleased to inform residents that compliance with all state and federal drinking water laws remains exemplary.  We are committed to delivering the best quality drinking water.  To that end, we remain vigilant in meeting the challenges of water system protection, water conservation and community education. To view the 2018 annual report, please click here.  [Note: annual reports issue by July of the following year]. To view the "UCMR3" report, which provides additional detailed water quality testing information, click here.

View quarterly water quality reports from Seattle Public Utilities (the provider of the City's potable water) -- Mercer Island water derives from the Cedar River Watershed system. 
Water Standard Details
Click here to view the most current version of the Water Standard Details.

Water Testing
Click here to view a list of local laboratories to contact for residential water testing.

Water System Plan
The purpose of the Water System Plan (WSP) is to examine the existing system and its operation, analyze system hydraulics, study current and projected future demands by computer modeling and develop a plan to meet the Cityís water system needs to the year 2035 and beyond. The drafted 2015 WSP has been reviewed and commented on by the Department of Health (DOH) and the Seattle Public Utilities (SPU).  Responses to both agencies were addressed in response letters provided by the City.  Revisions to various subjects and areas of the draft 2015 WSP were made in accordance to the agencies' review comments. The final 2015 WSP was adopted by City Council on October 4, 2016. 

A copy of the 2015 Water System Plan is available at City Hall. 
Or click here for a PDF copy of the complete 2015 WSP (LargeFile! 15 Mb).
Central Puget Sound Water Suppliers Forum
Click here to learn about the Forum's purpose, members and most commonly asked questions.
Emergency Well
The City developed the emergency well to supply Island residents with water for an extended period of time without significant assistance from outside during an emergency; the well water requires treatment before it is suitable for consumption. Click here for more information.

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