Such serial bonds shall bear interest at not more than six per cent per annum, payable semiannually, and shall be payable at such times, not exceeding forty-five years from their date, and at such places as shall be prescribed in the ordinance or resolution providing for their issuance. The bonds and their coupons shall be made payable in lawful money of the United States. The bonds shall mature annually or semiannually, and the first installment thereof shall be made payable not more than five years from the date thereof. The principal of and interest upon such bonds shall be payable solely from the revenues derived from the operation of the system or project for the purchase, construction, improvement, enlargement, extension or repair of which they are issued except that when a borrower improves, enlarges, extends or repairs any system or project named in § 6-21-50 the principal of and interest upon such bonds may be made payable from the revenues derived from the operation of the entire system or project. No bonds or coupon issued pursuant to this chapter shall constitute an indebtedness of the borrower within the meaning of any State constitutional provision or statutory limitations. It shall be plainly stated on the face of each such bond and coupon that it has been issued under the provisions of this chapter and that it does not constitute an indebtedness of the borrower within any State constitutional provisions or statutory limitation.

The bonds and coupons shall be executed in such manner and shall be substantially in the form provided in the authorizing ordinance or resolution.