The board of supervisors shall at the time and in the manner of levying other county taxes, levy and cause to be collected a tax upon the taxable real and personal property in the district, based upon the last equalized assessment roll of the county, sufficient to pay (a) the interest on bonds for that year, and the portion of the principal that is to become due before the time for making the next general tax levy, and (b) the amount necessary to maintain, operate, extend, or repair any work or improvements within the district, and to defray all other expenses incidental to the exercise of any of the district powers or to pay any existing obligations of the district. The aggregate taxes levied for any one fiscal year, other than those levied to pay the principal and interest on the bonds, shall not exceed one dollar ($1) on each one hundred dollars ($100) of the assessed valuation of taxable real and personal property in the district.