Cal. HSC § 6480.5

At any time within two years after a sanitary district consolidates with or annexes the territory of a district having powers and functions substantially identical to those of a sanitary district formed pursuant to this part, the board of directors of the sanitary district may, by resolution, increase the number of members of the board from five to seven, and may designate the first two additional members to serve on the enlarged board. If the board is enlarged subsequent to the consolidation with, or the annexation of the territory of, another district, the first two additional directors so designated shall be resident voters of such consolidated or annexed territory. The board shall determine the term of office of each of the new directors so appointed, but in no event shall such term designated by the board be for more than four years. The terms of office thus created shall be determined in such a manner as to keep as nearly equal as practicable the number of directors to be elected at each subsequent general district election. Upon the expiration of such term so designated by the board, the membership shall be filled at the next general district election and general district elections held thereafter for the election of officers of the district.

Any references to five members of the board in this part mean seven members as applied to a board increased in size pursuant to this section. In the same manner, references to three members mean four members and to two members mean three members, and references to a four-fifths vote mean a five-sevenths vote, as applied to an enlarged board.