Colo. Rev. Stat. § 37-48-158
To maintain, operate, and preserve ditches, canals, reservoirs, or other improvements made pursuant to this article and to strengthen, repair, and restore the same, when needed, for operation of any plan of water management, and for the purpose of defraying any incidental expenses of the subdistrict, the board of directors may, at the time of certification of the general district mill levy to the boards of county commissioners of the counties in which the district is located, certify also, to the boards of county commissioners of the counties in which said subdistrict or any part thereof is located, an additional assessment upon the taxable property within the subdistrict, not to exceed five mills for every dollar of valuation for assessment within said subdistrict, for the purpose of raising funds to be used for the maintenance and operation of the subdistrict's official plan. If there is a board of managers for the subdistrict, the amount of money needed to be raised by such assessment shall be certified by the board of managers to the district board of directors in time for inclusion of the amount in the district budget for the succeeding calendar year. Assessments so certified shall be levied by the boards of county commissioners of the counties in which said subdistrict is situate on the property of said subdistrict in their respective counties, to be collected by the county treasurers of the several counties and delivered to the treasurer of the district in like manner and with like effect as is provided for the collection and return of other assessments under this article. The whole assessment shall be due and payable as and when taxes for county purposes levied in the same year are due and payable. The said assessments shall be in addition to any special improvement assessment or special assessment that has been levied against benefits appraised for and on account of construction.
C.R.S. § 37-48-158