Any county in which a drainage district was organized and is continuing operations pursuant to statutes enacted prior to the effective date of this section¹ shall be authorized to impose an assessment upon real or personal property located within the boundary of the district as such district was organized upon the effective date of this section for the same purpose, based upon the assessed value of the property as determined by the current assessment roll of the county assessor in the county where the property is located. Properties that are exempt from ad valorem taxation are exempt from the assessment referred to within this section.