Colo. Rev. Stat. § 37-31-124
The board of directors has the power, without advertising for bids, to enter into a contract upon such terms as the board may regard as equitable, with any individual, partnership, corporation, or governmental entity or an irrigation or drainage district organized under the laws of this state or with more than one or with all of said parties, for the making of any surveys, plans, and specifications for a proposed drainage ditch, system, or works, or for the construction in whole or in part of such drainage ditch, system, or works, or for the joint use of any drainage ditch or drainage facilities; but no such contract involving an expenditure by said district of an amount in excess of twenty-five percent of the district's budget shall become effective and binding unless the question of making such contract has been submitted to and authorized at a general or special election of the qualified electors of the district.
C.R.S. § 37-31-124