Cal. Health & Saf. Code § 4730
The governing body of a sanitation district is a board of directors of not less than three members. The presiding officer of the governing body of each city, the whole or part of which is included in the sanitation district, is a member of the board. A member of the governing body of each sanitary district, the whole or part of which is included in the sanitation district, is a member of the board.
If the sanitation district includes territory which is unincorporated and not included in a sanitary district, then the presiding officer of the county board of supervisors is a member of the board.
The governing body of each city with a population of under 2,500,000, as found by the latest census, and the board of supervisors shall each select one of its members, other than its presiding officer, as an alternate director to act as a member of the district board in place of the presiding officer, or in place of the other member of the governing body of the city or county where there are two members from the city or county on the board of directors of the district, during such person's absence, inability, or refusal to act.
The presiding officer of the governing body of a city with a population of 2,500,000 or over shall select one of the other members of the governing body as an alternate director to act as a member of the district board in place of the presiding officer, or in place of the other member of the governing body of the city where there are two members from the city on the board of directors of the district, during such person's absence, inability, or refusal to act. The governing body of each sanitary district represented on the board of directors of a sanitation district shall select one of its members as an alternate director to act as a member of the district board in place of its regular director, or in place of the other member of the governing body of the sanitary district where there are two members from the sanitary district on the board of directors of the district, during such person's absence, inability, or refusal to act.
If the sanitation district includes unincorporated territory and all or part of one city and no sanitary district, or unincorporated territory and one sanitary district and no city, then the presiding officer and one other member of the board of supervisors are members of the board, unless the population included in the city or sanitary district is more than half of the population of the whole sanitation district, in which case the presiding officer of the board of supervisors and the presiding officer and one other member of the governing body of the city or two members of the governing body of the sanitary district, as the case may be, constitute the board of directors.
If the total number of cities and sanitary districts included in the sanitation district in whole or in part is two and if the sanitation district does not include any territory not in cities or sanitary districts, then the district board includes the presiding officer and one other member of the governing body of the city or two members of the governing body of the sanitary district having the greatest population and the presiding officer of the governing body of the city or one member of the governing body of the sanitary district having the least population.
If the total number of cities and of sanitary districts wholly or in part within the sanitation district is two or more, and if, in addition, the district contains unincorporated territory, then the district board includes the presiding officer of the board of supervisors, the presiding officer of the governing board of each city, and a member of the governing board of each sanitary district.
If the district includes no territory which is in cities or sanitary districts, then the county board of supervisors is the board of directors of the district.
If the territory of the district lies wholly within a city, the legislative body of said city is the board of directors of the district.
A city within a sanitation district, the sewered portion of which city lies entirely within a sanitary district, shall have no representation on the board.
Notwithstanding the foregoing provisions of this section, whenever a sanitation district includes unincorporated territory and all or part of one city and no sanitary district, the governing body of such city may designate the board of supervisors of the county as the district board of directors, unless the population of the incorporated portion of the sanitation district is more than half of the population of the whole district. If the population of the incorporated portion of the sanitation district is more than half of the population of the whole district, the board of supervisors of the county may designate the governing body of the city as the district board of directors.
The term "sanitary district" as used in this section shall mean a sanitary district formed prior to the formation of the sanitation district in which it is included in whole or in part. The term "sanitary district" as used in this section shall also include a county water district which on or before July 1, 1977, assumed the responsibilities, rights, duties, assets, liabilities, and obligations of a sanitary district which at the time of such assumption had representation on the board of directors of the sanitation district by the provisions of this section.
Ca. Health and Saf. Code § 4730