Cal. Water Code - WAT § 47550. Section 47550.
Upon the inclusion of any land within a district pursuant to Chapter 2 of Part 10 of this division an assessment shall be levied upon the land, the amount of the assessment against each tract or parcel to be the amount, as nearly as can be determined, of all assessments, other than those levied under the authority of Chapter 7 of this part, which would have been levied against the tract or parcel if it had been included in the district from its organization.