It shall be the duty of the district engineer, on being notified by a contractor that the work, or any installment thereof, provided for in his contract, is completed, to examine the same, and if he finds that it is completed according to the specifications of the report of the engineer and viewers, as confirmed, as provided in this chapter, he shall accept the same, and give to such contractor a certificate of acceptance, stating that such installment or contract is completed according to such specifications, and file a duplicate thereof in the office of the clerk of the county commission, and on presentation by any contractor of claim for payment for work performed, or any installment thereof, as provided by his contract, accompanied by such engineer’s certificate, the county commission shall audit the claim, and if the same is in accordance with such claimant’s contract and the work has been performed within the time therein specified, it shall draw a warrant upon the county treasurer for the amount thereof, payable out of the funds of the district available for the payment of such charges.