When it is necessary to conduct the sewage of a district or to acquire a supply of water beyond the district limits and to construct mains or aqueducts to conduct water or sewage to the district limits, the board by grant, purchase, or condemnation proceedings may acquire private property over which to construct the sewer, or upon and over which to establish facilities for obtaining and storing such water supply and aqueducts or mains for conducting water to the corporate limits. Public property may be acquired for those purposes by grant or purchase from the government or public corporation owning the property. The cost of acquiring such property and building such sewer or other facilities upon or over the property may be included in the cost of construction or acquisition of a district waterworks or sewerage system and in the district’s special assessments levied, or the entirety of such a project may be completed as an improvement to an existing waterworks or sewage system and special assessments may be levied for that purpose in accordance with the provisions of this title.