Wash. Rev. Code § 35.82.110
An authority shall have the right to acquire by the exercise of the power of eminent domain any real property which it may deem necessary for its purposes under this chapter after the adoption by it of a resolution declaring that the acquisition of the real property described therein is necessary for such purposes. An authority may exercise the power of eminent domain in the same manner and under the same procedure as now is or may be hereafter provided by law in the case of other corporations authorized by the laws of the state to exercise the right of eminent domain; or it may exercise the power of eminent domain in the manner now or which may be hereafter provided by any other applicable statutory provisions for the exercise of the power of eminent domain. Property already devoted to a public use may be acquired in like manner: PROVIDED, That no real property belonging to the city, the county, the state or any political subdivision thereof may be acquired without its consent.
RCW 35.82.110
Eminent domain: Title 8 RCW.