Cal. Sts. & High. Code § 25410

The treasurer of the district shall annually determine the amount of money necessary to be raised for the payment of principal and interest coming due each fiscal year upon any outstanding revenue bonds. The treasurer shall add to that amount a sum sufficient, in his judgment, to cover anticipated delinquencies and the resulting sum shall be levied upon all of the property taxable for county purposes, in the several counties composing the district, according to the percentages and proportions established for each county.