Wash. Rev. Code § 90.03.040
The beneficial use of water is hereby declared to be a public use, and any person may exercise the right of eminent domain to acquire any property or rights now or hereafter existing when found necessary for the storage of water for, or the application of water to, any beneficial use, including the right to enlarge existing structures employed for the public purposes mentioned in this chapter and use the same in common with the former owner, and including the right and power to condemn an inferior use of water for a superior use. In condemnation proceedings the court shall determine what use will be for the greatest public benefit, and that use shall be deemed a superior one: PROVIDED, That no property right in water or the use of water shall be acquired hereunder by condemnation for irrigation purposes, which shall deprive any person of such quantity of water as may be reasonably necessary for the irrigation of his or her land then under irrigation to the full extent of the soil, by the most economical method of artificial irrigation applicable to such land according to the usual methods of artificial irrigation employed in the vicinity where such land is situated. In any case, the court shall determine what is the most economical method of irrigation. Such property or rights shall be acquired in the manner provided by law for the taking of private property for public use by private corporations.
RCW 90.03.040
Eminent domain by corporations: Chapter 8.20 RCW.