The annual assessment may include a levy sufficient to raise any or all of the following:
(a) The amount that the board determines is necessary for a depreciation fund for the replacement or reconstruction of any specific units of its works.
(b) The amount that the board determines is necessary, not to exceed 4 percent of the aggregate value of the land according to the latest equalized assessment, and not otherwise provided for, to pay for the maintenance and operation of the district for the ensuing calendar year.
(c) The amount that the board determines is needed to be raised by assessment for any other district purposes not exceeding 4 percent of the aggregate value of the land according to the latest equalized assessment.
(d) An amount not exceeding 1 percent of the total assessed value of the land that the board deems proper to pay into the bond fund to be used for the purchase of bonds of the district not yet due or for payment into a fund to pay such bonds as they become due.