(a) In accordance with Section 49.108, Water Code, the district may impose a tax other than an operation and maintenance tax and use the revenue derived from the tax to make payments under a contract after the provisions of the contract have been approved by a majority of the district voters voting at an election held for that purpose.
(b) A contract approved by the district voters may contain a provision stating that the contract may be modified or amended by the board without further voter approval.