California Code, Water Code - WAT § 35190

(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. Such divisions shall be as nearly equal in population as practicable; provided, however, that if there is uninhabited land, which shall be defined as land having 12 or less registered voters residing therein in excess of 3,000 contiguous acres within any improvement district, such land may be designated by the board of directors as a division, and in such event elections for director for such division, which director need only be a holder of title to land within such division, shall be conducted in accordance with the provisions of Article 1 (commencing with Section 35000) of Chapter 1 and Chapter 2 (commencing with Section 35100) of this part.

(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 by resolution may, 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.