California Code, Government Code - GOV § 54711

(1) The amount of the assessment imposed on any parcel of property shall be related to the benefit to the parcel which will be derived from the provision of the service.  Except as provided in subdivision (d) or (e) of Section 54715, in the case of a benefit assessment for flood control services, the benefit may be determined on the basis of the proportionate storm water runoff from each parcel.  In the case of an assessment for the maintenance of streets, roads, or highways, the benefit may be in proportion to the estimated traffic volume to be generated by each parcel assessed, or any other reasonable basis as determined by the legislative body.  In the case of an assessment to cure bond fund deficiencies pursuant to Section 54710.3, all parcels subject to the assessment may be assumed to benefit equally from the jurisdiction's improved ability to finance special benefit projects through assessments at lower cost, due to the added security provided by the assessment levied pursuant to this chapter.

(2) The annual aggregate amount of the assessment shall not exceed the estimated annual cost of providing the service, except that the legislative body may, by resolution, determine that the estimated cost of work authorized pursuant to subdivision (b) of Section 54710 is greater than can be conveniently raised from a single annual assessment and order that the estimated cost shall be raised by an assessment levied and collected in installments over a period not to exceed five fiscal years.

(3) The revenue derived from the assessment shall not be used to pay the cost of any service other than the service for which the assessment was levied.