The Department of the Interior, Bureau of Reclamation proposes to construct a project to provide drinking water to local communities and rural water systems in northwestern North Dakota. The project would be designed to supply bulk water to serve the municipal, rural, and industrial water needs through 2060.The proposed action would include the construction of components needed to provide reliable, high-quality drinking water to existing infrastructure for distribution to water users in the service area. This Final Supplemental Environmental Impact Statement supplements the 2008 Final Environmental Impact Statement on Water Treatment prepared by Reclamation. It has been prepared pursuant to the National Environmental Policy Act to analyze and disclose the effects of the proposed action on environmental and human resources. Four action alternatives and a No Action Alternative are evaluated. The Missouri River and Groundwater Alternative is the preferred alternative. This alternative includes an intake at Lake Sakakawea, within Reclamation’s Snake Creek Pumping Plant, and a Biota Water Treatment Plant in Max, North Dakota. Biota treatment, using conventional treatment processes, is included as a means of reducing the Project-related risk of transferring aquatic invasive species from the Missouri River basin to the Hudson Bay basin.