This bill, titled the Dry-Redwater Regional Water Authorization Act, aims to establish the Dry-Redwater Regional Water Authority System. Its primary purpose is to ensure a safe and adequate municipal, rural, and industrial water supply for citizens in Dawson, Garfield, McCone, Prairie, and Richland Counties in Montana, as well as McKenzie County in North Dakota. The Secretary of the Interior is authorized to carry out this project, substantially in accordance with a Bureau of Reclamation feasibility study, and must enter into a cooperative agreement with the Dry-Redwater Regional Water Authority for the planning, design, and construction phases. The federal share of these costs is capped at 75 percent of the total, or a lesser amount determined by the Secretary. Federal funds can be used for various facilities, including water pumping, treatment, storage, transmission pipelines, and electrical power infrastructure, but are explicitly prohibited for the system's operation, maintenance, or replacement. A key provision ensures the availability of power from the Pick-Sloan Program for the Water System's operational requirements. The Administrator of the Western Area Power Administration is directed to provide this power at the firm power rate, provided the Water System operates on a not-for-profit basis. The Authority will be responsible for power charges and non-Federal delivery costs, including funding any necessary upgrades to the transmission and distribution systems. The bill explicitly states that it does not preempt or affect any State water law or a State's authority to manage water resources. For funding, it authorizes the appropriation of $602,000,000 for the project's planning, design, and construction for fiscal years 2027 through 2037, with provisions for adjusting this amount based on cost indexing and unforeseen market volatility.