Idaho Code § 42-110: Right to divert water.

The proprietors of any ditch, canal or conduit, or other works for the diversion and carriage of water, whose right relative to the quantity of water they shall be entitled to divert by means of such works shall have been established by any valid claim, permit, license or decree of court, shall be entitled to such quantity measured at the point of diversion, subject, however, to all prior rights. Water diverted from its source pursuant to a water right is the property of the appropriator while it is lawfully diverted, captured, conveyed, used, or otherwise physically controlled by the appropriator.