Mont. Code Ann. § 85-2-416

A person desiring to purchase surplus water pursuant to 85-2-415 shall, at the person's own cost and expense, construct or dig the necessary flumes or ditches to receive and convey the surplus water desired by the person and pay or tender to the person having the right to the use, sale, or disposal of that water an amount equal to the necessary cost and expense of tapping any gulch, stream, reservoir, ditch, flume, or aqueduct and putting in gates, gauges, or other proper and necessary appliances usual and customary, and until that work is done, the delivery of the surplus water may not be required as provided in 85-2-415.