Water Utility
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 information on the program and your responsibilities.
Water Utility Billing
Do you have questions about your water bill? Click here for more information.
Watersheds: The Source of Our Water
The region’s 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 snow melt. 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
Learn more about rebates and conservation tips for business, home, and garden.
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 2022 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 City’s water system needs to the year 2035 and beyond. The drafted 2015 WSP was 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. Click here to download the 2015 WSP. The 2022 Limited Water System Plan Update was adopted by City Council on September 20, 2022. Click here to download the Limited Update.
Water Supply Forum
The Water Supply Forum addresses current and future water supply issues, including supply system resiliency, planning, policy and regulation, and environmental stewardship. It is comprised of representatives of public water systems and local governments in Washington state’s central Puget Sound region. Working cooperatively, the Forum’s members promote the reliable delivery of safe, clean water throughout the region. Click here to learn more.
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.
