Wash. Rev. Code § 87.03.080
An election of directors in an irrigation district shall be held on the second Tuesday of December of each year, and the term of each director shall be three years from the first Tuesday of January following his or her election. The directors elected at the organization election shall serve until their successors are elected and qualified. At the first annual election occurring thirty days or more after the date of the order establishing the district, there shall be elected directors to succeed those chosen at the organization election. If the board consists of three directors the candidate receiving the highest number of votes shall serve a term of three years; the next highest, two years; and the next highest, one year. In case of five directors, the two candidates receiving the highest number of votes shall each serve a term of three years; the next two highest, two years; and the next highest, one year; or until successors are elected and qualified. In case of seven directors, the three candidates receiving the highest number of votes shall each serve a term of three years, the next two highest, two years, and the next two highest, one year, or until their successors are elected and qualified. Whenever a district with three directors desires to increase the number of its directors to five directors or whenever a district with five directors desires to increase the number of its directors to seven directors, the board of directors, acting on its own initiative or on the written petition of at least twenty electors of the district, shall submit the question to the electors of the district at a regular or special district election. In the event the electors by a majority of the votes cast favor an increase in the number of directors, there shall be elected at the next annual district election two additional directors. The person receiving the highest number of votes shall serve for a three year term and the next highest, a two year term.
The number of directors may be decreased to five or three, as the case may be, substantially in the same manner as that provided for the increase of directors. In case of three directors the term of one director only shall expire annually.
RCW 87.03.080