All school, granted, and other state lands, and lands owned by the United States, when legally possible, and all county, city and other municipally owned property, not used for governmental purposes, and all privately owned lands within the corporate limits of any county, school district, city or other municipal corporation included within the operation of the district and benefited by the district improvement, shall be liable for assessment as provided herein for other property.
RCW 86.09.526