La. Stat. tit. 33 § 4113
After expiration of the period within which property owners may pay their total assessment without interest, the sewerage and water board of New Orleans may by resolution adopted by the affirmative vote of not less than three-fourths of its entire membership authorize an issue of certificates to an amount not exceeding the aggregate amount of the assessments levied against the owners of property in the defined drainage area less the aggregate amount of such assessments theretofore paid by the property owners. Such certificates shall be payable solely out of the assessments levied by resolution of the sewerage and water board of New Orleans upon the properties in a defined area. The form of said certificates and the manner of their execution shall be prescribed by the sewerage and water board of New Orleans, and shall state on their face that they are obligations of the sewerage and water board, payable solely out of the assessments levied by a resolution of the sewerage and water board upon the properties in a defined drainage area, which resolution shall be identified by its title and date of adoption. Certificates issued under the authority of this Section shall be exempt from all taxation for state, parish, municipal or other local purposes.
La. R.S. § 33:4113