Whenever there are outstanding any bonds of the county representing moneys heretofore or hereafter expended upon the waterworks system, the funds in the county treasury to the credit of the board of water supply shall be drawn upon by the county treasurer to the extent necessary from time to time to provide for payment of the bonds and the interest thereon according to the tenor and terms thereof, the moneys so drawn to be placed to the credit of the appropriate sinking fund and used for such purposes.
HRS § 54-23