25 C.F.R. § 134.1
In pursuance of the act of February 14, 1920 (41 Stat. 409; 25 U.S.C. 386 ), regulations governing partial payment of construction charges on Indian irrigation projects, with the exception of certain ones mentioned therein, where approved by the Department June 21, 1920, and require that each owner of irrigable land under any irrigation system constructed for the benefit of Indians under provisions of law requiring reimbursement of the cost of such system and to which land, water for irrigation purposes can be delivered from such system, shall pay, on or before November 15, 1920, a sum equal to 5 percent of the per acre cost, as of June 30, 1920, of the construction of the system under which such land is situated. The per acre cost of a given system as of June 30, 1920, shall be determined by dividing the total amount expended for construction purposes on such system up to that day by the total area of land to which water for irrigation purposes can be delivered on that date; and on November 15 of each year following the year 1920, until further notice, the land owners, as therein prescribed, shall pay 5 percent of the per acre construction cost as of June 30, of the current year, such per acre cost to be determined by dividing the cost of the system to June 30 of that year by the total area of land to which water for irrigation purposes can be delivered from the system on that date. Provision is contained that no payments shall be required under the regulations in behalf of lands still in process of allotment or prior to the issuance of the first or trust patent therefor, nor for lands reserved for school, agency, or other administrative purposes where the legal title still remains in the United States.
25 C.F.R. § 134.1