Sec. 9. (a) In fixing the revenues of the department required for operation and maintenance, the board shall consider the cost of the operation and maintenance of the department.
(b) If a surplus is accumulated in the operating and maintenance account, the board may transfer any excess over that surplus to:
(1) the depreciation account, to be used for any improvements, extensions, or additions to the storm water system; or
(2) the bond and interest redemption account.