The Dakota Mainstem Water Supply Project Feasibility Study Act aims to assess the possibility of building a water supply project for municipal, rural, and industrial use in a specific region. This area includes parts of South Dakota, Iowa, Nebraska, and Minnesota. The main goal is to ensure that communities in this region have reliable access to water. The key provisions of this act require the Secretary of the Interior to conduct a study in partnership with the Dakota Mainstem Regional Water System, a nonprofit organization.