All contracts entered into for any work provided for in this chapter shall be entered into in the name of the district and shall be executed on the part of the district by the chairman of the board of directors and countersigned or attested by the secretary. When the contract is signed by the contractor, it shall be filed in the office of the secretary of the district. Contracts for materials or for construction of any nature shall require the work to be done or the materials to be furnished in accordance with, and pursuant to, plans and specifications on file with the secretary. There shall be reserved in each such contract for construction the right of the board of directors, in case of the improper construction of such work, to suspend work thereon at any time, and to relet the contract therefor, or to order a reconstruction of said work or any part thereof improperly done. Each such contract shall state the time on or before which such work must be completed and shall state how such contract will be paid.