For lands irrigable under any irrigation system or reclamation project the Secretary of the Interior may fix maintenance charges which shall be paid as he may direct, such payments to be available for use in maintaining the project or system for which collected: Provided further, That all moneys expended under this provision shall be reimbursable where the Indians have adequate funds to repay the Government, such reimbursements to be made under such rules and regulations as the Secretary of the Interior may prescribe: Provided further, That the Secretary of the Interior is authorized and directed to apportion the cost of any irrigation project constructed for Indians and made reimbursable out of tribal funds of said Indians in accordance with the benefits received by each individual Indian so far as practicable from said irrigation project, said cost to be apportioned against such individual Indian under such rules, regulations, and conditions as the Secretary of the Interior may prescribe.