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 is in need of maintenance and at risk from potential natural disaster or process equipment breakdown. The treatment plant retrofit will provide the community with clean, reliable drinking water for decades to come.

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

As of June 2021, design for the new plant reached 60% completion and will be finished by the end of the year. The construction phase is schedule to begin in mid-October 2021.



Lewiston, Idaho


City of Lewiston

Contract Amount

$27.5 million


2021 - present

Anticipated Completion

June 2024

Project Highlights

Since 1924 the City of Lewiston has done a tremendous job keeping the aging plant in service. However, the growing community needs a larger, more efficient plant that will allow for future growth. After presenting three options to the city to rectify their aging plant, the team decided to build an entirely new plant in the footprint of the existing sedimentation basin. This creative approach was presented by IMCO’s team and contributed to the City’s decision to select IMCO as their partner.