15-6-205. State water conservation projects exempt. All lands acquired and held by the department of natural resources and conservation or the state of Montana for use in connection with water conservation projects constructed or to be constructed under the laws of this state are exempt from taxation, and the county treasurer shall cancel all taxes remaining unpaid on the land for the year in which the land is acquired and for all previous years. The taxes may be canceled only if a tax certificate has not been issued or, if a tax certificate has been issued, it was issued to the county and an assignment of the certificate of sale has not been made by the county prior to the time that the land was acquired by the department.