Idaho Code § 42-3210
The board shall meet regularly once each month at a time and in a place to be designated by the board. Special meetings may be held as often as the needs of the district require, on notice to each member of the board. Three (3) members of the board shall constitute a quorum at any meeting. Any vacancy on the board shall be filled by the remaining members or member of the board, the appointee to act until the next biennial election when the vacancy shall be filled by election. If the board shall fail, neglect or refuse to fill any vacancy within thirty (30) days after the same occurs, the court having jurisdiction shall fill such vacancy. In the event the board has created director zones and is unable to appoint a board member from the zone vacated, the board may appoint a person-at-large who is an elector of the water and/or sewer district to serve as director of the zone where the vacancy occurred.
Idaho Code § 42-3210