FAQs

On April 3, 2024, the City learned of a leaking underground Seattle Public Utilities water pipe. The leak created unstable soil conditions, which could have resulted in dangerous flooding if the soil were to move substantially and break the water line, putting homes at risk. After a geotechnical engineer reviewed the soil conditions, the City of Mercer Island notified residents in approximately 20 homes near 95th Court SE to evacuate their property. City and SPU crews were able to shut off the pipe, and all affected residents were allowed back in their homes.

With the pipe offline, this means that our water supply is reduced while crews from Mercer Island and SPU work to repair the pipe. Mercer Island is currently receiving enough water through a smaller backup supply line, but during the high-demand summer months it is possible that our demand will exceed current supply. To ensure we have sufficient supply to sustain water quality, safety, and firefighting requirements, it’s important that we all take steps to collectively conserve water. You can learn more about these water conservation needs here.

A repair is currently underway. You can learn more about it in the FAQ's below, and on this Let's Talk page.

A traditional repair of the pipe is challenging due to the site conditions. The location of the leak is on a very steep slope, in a difficult area to access with no adjacent roadway. As a result, SPU and the City have selected a liner solution that will insert a flexible liner inside the existing pipeline, spanning a total of 1,100 feet.

This approach does not require excavation on the slope. Instead, the liner will be inserted through two access points to the east and west of the leak location. When the liner is installed, it will include a leak detection system to ensure a rapid response if there is ever a subsequent issue with the pipe. Geotechnical engineers from the City and SPU have been closely evaluating the stability of the slope in considering this repair option to ensure the community’s safety.

The City has agreed to the liner plan and installation is scheduled to begin soon. 

The liner is the best repair option given the challenging geography of the area. Installing the liner does not require excavation on the steep slope, where there is no adjacent roadway or easy access. Likewise, this solution allows the City to resume use of the primary water line relatively quickly, is designed to be long-lasting, and provides a system for ongoing leak-detection. 

The liner uses state-of-the-art engineering to provide ample flexibility (up to 90-degree bends) with high durability, and it has been tested thoroughly by expert engineers to ensure its safety and reliability. This product has already been used in projects in Seattle and is being introduced into other Mercer Island utilities. It’s also made from materials that are stable, well-tested, and do not impact water quality.

The material is certified by several global standards to have no impact on water quality or safety.  

The liner being installed for this repair is the Primus Line W-Liner, which comprises three layers:  

• An inner layer made of polyethylene (PE), which is commonly found in home plumbing systems. 
• A middle layer made of aramid fabric, which is similar to Kevlar. This layer is not exposed to water. 
• An outer protective layer also made of PE. 

The Primus Line W-Liner is sourced and manufactured in Germany, which requires all potable water materials to be free of PFAS. There are no PFAS in the PE portion of the product that contacts our water supply. Liner information also indicates it is BPA-free. 

The liner does not adhere to the primary water pipe when it’s installed, and no glues, epoxies, heat, chemical curing or resins are used in its installation. Instead, the liner is “pulled” through the pipe and is secured at either end with steel fittings. Air pressure inflates the liner to its final diameter.

The Primus Line W-Liner is certified in accordance with many global standards to ensure it meets the highest requirements for potable water safety and quality. Importantly, it is certified according to ANSI/NSF/CAN 61, a classification set by the National Science Foundation and the American National Standard Institute to evaluate the health effects of materials, products, and systems that come into contact with drinking water.

The liner is designed to last up to 50 years and will provide sufficient water supply to Mercer Island while the City explores options for long-term pipeline replacement of the pipe in a new, more accessible location. 

It will take approximately one month to resume use of the primary water line after the liner installation process begins.

The City’s primary water line will be operational about one month after the liner is installed. The liner will greatly improve the flow of water to Mercer Island, and water modeling shows that it will provide sufficient supply to meet our demand.

It’s always good to conserve water when you can, and because the lined pipe will have less capacity than the unlined 24” pipe, we will continue to encourage general water conservation best practices.