The Secretary shall require, as conditions to any such loan, that the borrower contribute in money or materials, labor, lands, or interests in land, computed at their reasonable value, a portion not in excess of 10 per centum, of the construction cost of the distribution and drainage system (including all costs of acquiring lands and interests in land), that the plans for the system be in accord with sound engineering practices and be such as will achieve the purposes for which the system was authorized, and that the borrower agree to account in full in regard to all disbursements of borrowed funds and to return at once for application toward amortization of the loan all funds which are not expended in the construction of the distribution and drainage system. Every organization contracting for repayment of a loan under sections 421a to 421h of this title shall operate and maintain its distribution and drainage works in conformity with reasonable contractual requirements determined to be appropriate for the protection of the United States. The Secretary is hereby authorized to reconvey to borrowers all lands or interests in lands and distribution works transferred to the United States under the provisions of sections 421a to 421h of this title: Provided, That any reconveyance shall be upon the condition that the repayment contract of the borrower be amended to include such provisions as the Secretary shall deem necessary or proper to provide assurance of and security for prompt repayment of the loan. The head of any department or agency of the Government within whose administrative jurisdiction are lands owned by the United States the use of which is reasonably necessary for the construction, operation, and maintenance of distribution and drainage works under sections 421a to 421h of this title may grant to a borrower or prospective borrower under sections 421a to 421h of this title revocable permission for the use thereof in like manner as under sections 79 1