A.R.S. § 48-2366

If any member of the council or board of directors ceases to be a qualified district elector for land in the member's division or a resident of the district, or if the president, vice-president or an at large director ceases to be a qualified district elector for lands within the boundaries of the district or a resident of the district, the office shall thereupon become vacant. The council may by appointment fill a vacancy in the council and in the board of directors. The council shall adopt by-laws providing for the filling of vacancies in the office of president or vice-president.