(a) The interest and sinking fund consists of taxes collected for the fund. Money in the interest and sinking fund may be paid out only to:
(1) pay district bonds and satisfy and discharge interest on the bonds; and
(2) defray the expense of imposing a tax for the fund.
(b) The maintenance and improvement fund consists of money collected by assessment or other sources for:
(1) the maintenance of property owned or acquired by the district;
(2) necessary improvements to be made by the district; and
(3) the general purposes of the district.