Colo. Rev. Stat. § 31-25-505
When the governing body declares the same necessary for sanitary reasons, it may order the construction of district sanitary sewers in districts to be prescribed by ordinance so as to connect with any public or district sewer or with some natural drainage or disposal plant. Such districts, by like authority, may be divided into subdistricts or enlarged, diminished, or otherwise altered by ordinance at any time in accordance with the provisions of this part 5. The contract for district sewers may include all necessary manholes, inlets, and appurtenances and such mains of such reasonable extent outside the district as may be necessary to connect the district with a public sewer or some natural drainage or disposal plant. Contiguous municipalities may unite in the construction of a common sewer or cooperate in such construction or extend to each other the right to use any sewer constructed or to be constructed when such use may be deemed necessary for the discharge of the sewage of either, and such cooperation, common construction, or use shall be upon such terms as regards the apportionment of cost as may be agreed upon between the governing bodies of such contiguous municipalities.
C.R.S. § 31-25-505
This section is similar to former § 31-25-526 as it existed prior to 1975.