The board of water management commissioners may secure and use men, equipment and materials under the supervision of the water management engineer to construct, excavate and complete all or any of the works of improvements which may be needed to carry out the plan of water management, or it may, in its discretion, let contracts therefor, either as a whole or in part. The board of commissioners shall fix the time and place of letting contracts for the construction of the improvements and cause notice thereof, containing a description of the work to be let, to be made by publication in three consecutive issues of some weekly newspaper (if such there be) of general circulation published in the county in which the district is organized and by at least one insertion in some contractor's or trade journal and by such additional publication elsewhere as the board of water management commissioners may deem expedient, the last insertion to be at least 10 days before the day of the letting. On the date appointed for the letting, the board of water management commissioners together with the water management engineer shall convene and let the proposed work either in whole or in sections as they may deem most advantageous for the district. They shall have the right to reject any and all bids and to readvertise the work if in their judgment the interests of the district will be served by so doing. The successful bidder shall be required to enter into contract with the board of commissioners and to execute a bond for the faithful performance of such contract with sufficient sureties in favor of the water management district in an amount not less than 25 percent of the estimated cost of the work awarded to him. The contract shall be based on the plans and specifications submitted by the engineer or other competent authority in the final report as adopted by the board of water management commissioners, the original of which shall remain on file in the office of the court of probate and shall be open to inspection by all prospective bidders. All bids shall be submitted sealed and shall not be opened except under the authority of the board of water management commissioners and on the date and at the hour therefor appointed for opening the bids. In case the water management commissioners are installing the works of improvement with the assistance of some organization or agency, engineering and other assistance necessary in connection with letting contracts or otherwise installing the works of improvement may be furnished by the cooperating organization or agency. In such case, the letting of contracts will be handled in a manner agreeable to both the water management commissioners and the organization or agency involved.