Colo. Rev. Stat. § 37-27-102
The lands within the boundaries of any city or town organized and existing under the general laws of this state or under article XX of the state constitution requiring drainage in whole or in part and susceptible of drainage by the drainage ditch, system, or works of any drainage district or proposed drainage district organized or proposed to be organized pursuant to the laws of the state of Colorado relating to the formation of drainage districts may be included within and made a part of any such drainage district upon the presentation to the board of directors of such district, or to the proper board of county commissioners, in case such district has not been organized, of a petition for such inclusion signed by a majority of the owners of such lands, whether residents or nonresidents of such city or town, as well as by the owners in the aggregate of the majority of the total number of acres of such land to be included, exclusive of the land occupied by public streets and alleys, public parks, and any other lands owned by any municipality. Such city or town shall bear the expense of the drainage of all area included with the streets, alleys, public parks, or other lands owned by it. It is the duty of the city council or board of trustees of such city or town to annually certify the amount necessary to pay the drainage assessments as authorized by said drainage district to the taxing tribunal, with instructions to such taxing tribunal to make a levy against the taxable property within such city or town for such purpose as provided by law in other cases of special assessment. Any inclusion of the lands within any city or town shall be subject to all of the provisions and conditions of articles 20 to 30 of this title.
C.R.S. § 37-27-102