Idaho Code § 42-908

Wherever two or more persons take water from any main ditch, canal or reservoir, at the same point, to be conveyed to their respective premises for any distance through the same lateral or distributing ditch, as provided in section 42-905[, Idaho Code], the person to be selected by such parties on or before April first of each year, as provided in section 42-907[, Idaho Code], may be selected and appointed by a written instrument designating such person, signed by the majority of such persons so using the said ditch for their said water, and filed with the watermaster or other managing agent or director of such main canal, ditch or reservoir.