Lewiston Water Treatment Plant Progressive Design-Build

Project Summary

The City of Lewiston selected the IMCO/Stantec design-build team to retrofit the existing 100-year-old plant, which was in need of maintenance and at risk from potential natural disaster or process equipment breakdown. The treatment plant retrofit provides the community with clean, reliable drinking water for decades to come.

As the design-build lead, IMCO partnered with Stantec Engineering to design and deliver this project. The project required an innovative approach, and the facility had to provide water to the community of 32,000 throughout the construction process. The existing plant was largely demolished, and water was provided via a combination of surface wells and mobile water treatment trailers. The mobile system augmented the wells to meet peak demands during the summer irrigation season. The new membrane treatment plant had the flexibility to deliver up to 10 million gallons per day (MGD), with space to expand to 16.7 MGD.

As of May 2023, the Lewiston Water Treatment Plant team reached the end of the final acceptance phase, collaborating with the City of Lewiston to work through challenges. The facility is now operational and delivering water to the community.



Lewiston, Idaho


City of Lewiston

Contract Amount

$27.5 million


2021 - 2023

Project Highlights

The Lewiston water treatment plant retrofit project has been recognized by the DBIA with a National Award of Merit in the water/wastewater category. IMCO’s design-build team used a creative approach to construction, employed the benefits of the progressive design-build delivery method to navigate challenges caused by the pandemic, and called upon incredible teamwork between the City of Lewiston, IMCO, Stantec, owner representative Brown and Caldwell, and Control Systems Technologies.