Annual Water System Improvements

The City’s water distribution system includes more than 113 miles of water mains of varying age, size, material, and condition.

Most of the system is composed of cast iron and ductile iron pipe. There is also nearly five miles of asbestos-cement (AC) pipe and one mile of steel pipe within the City's water distribution system.

Each year, the City identifies and undertakes projects to replace aging cast iron and AC pipe throughout the system.

AC Pipe vs. Cast Iron Pipe

Pressurized asbestos-cement (AC) pipe is a material known for developing leaks and breaks as it nears the latter part of its expected life. The AC pipe in the Mercer Island water system was primarily installed in the 1950s and 1960s, making it some of the oldest piping within the distribution system.

Cast iron pipe in the Mercer Island water system was primarily installed in the late 1950s and early 1960s. Some of the older cast iron piping is brittle, undersized, and known for developing leaks and breaks as it nears the latter part of its expected life.

2024 Water System Improvements - Cast Iron Pipe Replacements

The 2024 Water System Improvement project is part of our yearly water system improvement program to replace under-sized and aging cast iron water mains. The City expects to replace over 6,000 LF of cast iron water mains.

Along with water main replacement, this work includes two stub-outs for future connections in the Town Center, and storm drainage improvements within the neighborhood between SE 46th and SE 47thStreet west of Island Crest Way. The streets in this neighborhood will be repaved in 2025 as part of the City's residential street resurfacing program.

This work also encompasses water main replacement along SE 42nd Street near the shoreline of Lake Washington, which requires additional permitting, some possible slope restoration and drainage improvements, as well as easement acquisitions.

Learn more about the project here.

2024 AC Water Main Replacement

The purpose of the AC water main project is to systematically eliminate all AC water mains within the City of Mercer Island over a six-year period by replacing approximately 5,000 feet of AC pipe per year. 2024 replacements are scheduled for:

• SE Gallagher Hill Rd (3700 Block to 3600 Block)
• Greenbrier Lane (SE 40^th St, north to Gallagher Hill Rd)
• SE 40^th St from Greenbrier Lane to 93^rd Ave SE
• 93^rd and 94^th Ave SE from SE 40^th St to SE 43^rd St
• Crestwood Place

Learn more about the project here.