Colo. Rev. Stat. § 31-12-121
Any municipality, as a condition precedent to the supplying of municipal services pursuant to contract, may require a contemporary agreement by such consumers, who are owners in fee of real property so supplied, to apply for or consent to the annexation of the area to be supplied with such municipal services to the supplying municipality at such future date as the area supplied, or any portion thereof, becomes eligible for annexation pursuant to the provisions of this part 1. The agreement to annex shall be enforceable by an action for specific performance filed in the district court of the judicial district containing all or part of the supplying municipality. A memorandum of such agreement, setting forth the names of the owners in fee of real property supplied and the legal description of such area, shall be recorded in the office of the county clerk and recorder of the county in which such area is located and shall constitute constructive notice of such agreement to all persons not parties thereto. In no event shall the board of directors of any quasi-municipal corporation organized under part 5 or 6 of article 25 of this title, article 8 of title 29, part 2 of article 20 of title 30, or title 32 (except article 8), C.R.S., or any other law of this state be permitted to obligate or require property owners within any such district to sign any such agreement in order to obtain water service from a municipality.
C.R.S. § 31-12-121
This section is similar to former § 31-8-121 as it existed prior to 1975.