Colo. Rev. Stat. § 37-27-101
Upon petition of the owner of a tract of land and the payment of a sum equal to the past due assessments upon the same after a classification thereof upon a graduated scale by the board of directors as provided in section 37-23-101, so that the tract is upon an equal footing with other lands of the district, the board of directors may authorize the inclusion of any tract of land contiguous to the existing boundaries of said district and capable of being drained by said drainage system, and thereupon said lands shall become liable for all future assessments which may become due or are levied for drainage purposes within said drainage district, and the cost of any such proceeding for the inclusion of land shall be borne by the applicant.
C.R.S. § 37-27-101