Okla. Stat. tit. 82 § 1085.21
Whenever any project or plan for the construction or enlargement of any dam, reservoir or other structure includes within its design and specifications provisions for the development of water supplies for domestic, municipal, agricultural, industrial and other purposes the Commission is hereby directed to negotiate with the municipalities or other local interests of this state and its agencies and the federal government or its responsible agency, department or instrumentality for the purpose of determining the cost of reimbursing the federal government for the allocated cost of including such municipal, agricultural and industrial water storage within such construction. Any available storage for such purposes which cannot reasonably be used within the present or estimated future firm demands of local users may be contracted for by the Commission in order to assure the federal government that such added cost will be provided as authorized by federal law, and that necessary funds for any charges shall be paid by the Commission to the federal government pursuant to such contract and applicable federal law after examination and determination by the Oklahoma Water Resources Board that such charges are in harmony with existing federal law and policy at the time that the projects are built and the contracts between the Commission and the federal government are executed. In cases where all necessary costs to provide maximum conservation storage in a site cannot be contracted for between the federal government and the Commission because of limitations on the participation by the federal government, the Commission shall have the authority to provide funds covering those costs.
Okla. Stat. tit. 82, § 1085.21