Cal. Health & Saf. Code § 6550.12
Any moneys required to be raised from taxes for the purpose of paying the principal of and interest on bonds of the district for an improvement district shall be derived exclusively from an annual tax upon the taxable property in the improvement district of such sanitary district, and all the taxable property within the improvement district of such sanitary district shall be and remain liable to be taxed for such payments. The district board shall annually, at the time and in the manner of levying other district taxes, levy and cause to be collected a tax upon the taxable property in the improvement district, based upon the last equalized assessment roll of the district, 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. Such bonds and the interest thereon shall not be taxable in this state.
Ca. Health and Saf. Code § 6550.12