Cal. Health & Saf. Code § 4809.3
Bonds issued as bonds of the district for an improvement district therein and the interest thereon shall be paid by revenue derived exclusively from an annual tax upon the real property in the improvement district of such county sanitation district, and all the real property within the improvement district of such county sanitation district shall be and remain liable to be taxed for such payments. The board of supervisors of the county shall annually, at the time and in the manner of levying other county taxes, levy and cause to be collected a tax upon the taxable real property in the improvement district, based upon the last equalized assessment roll of the county sufficient to pay the interest on the bonds for that year and such portion of the principal as is to become due before the time for making the next general tax levy. Said bonds and the interest thereon shall not be taxable in this State.
Ca. Health and Saf. Code § 4809.3