California Code, Water Code - WAT § 35245

(a) The board of directors shall, by resolution, divide the district into as many divisions as there are directors and assign a number to each division. Divisions shall be as nearly equal in population as practicable.

(b) After approving the election of directors by divisions, the board of directors shall, by resolution, not less than 120 days prior to the next general district election, designate which divisions shall elect directors at that election to succeed the directors whose terms then expire. The remaining divisions shall elect directors at the general district election next following that election.

(c) Each director elected by division shall be a resident of that division.

(d) The board of directors may, by resolution, at any time after initially dividing the district into divisions, but not less than 120 days before a general district election, change the boundaries of the divisions to keep them as nearly equal in population as practicable.