Wash. Rev. Code § 84.34.220
In accordance with the authority granted in RCW 84.34.210, a county, city, town, metropolitan park district, metropolitan municipal corporation, nonprofit historic preservation corporation as defined in RCW 64.04.130, or nonprofit nature conservancy corporation or association, as such are defined in RCW 84.34.250, may specifically purchase or otherwise acquire, except by eminent domain, rights in perpetuity to future development of any open space land, farm and agricultural land, and timberland which are so designated under the provisions of chapter 84.34 RCW and taxed at current use assessment as provided by that chapter. For the purposes of chapter 243, Laws of 1971 ex. sess., such developmental rights shall be termed "conservation futures". The private owner may retain the right to continue any existing open space use of the land, and to develop any other open space use, but, under the terms of purchase of conservation futures, the county, city, town, metropolitan park district, metropolitan municipal corporation, nonprofit historic preservation corporation as defined in RCW 64.04.130, or nonprofit nature conservancy corporation or association, as such are defined in RCW 84.34.250, may forbid or restrict building thereon, or may require that improvements cannot be made without county, city, town, metropolitan park district, metropolitan municipal corporation, nonprofit historic preservation corporation as defined in RCW 64.04.130, or nonprofit nature conservancy corporation or association, as such are defined in RCW 84.34.250, permission. The land may be alienated or sold and used as formerly by the new owner, subject to the terms of the agreement made by the county, city, town, metropolitan park district, metropolitan municipal corporation, nonprofit historic preservation corporation as defined in RCW 64.04.130, or nonprofit nature conservancy corporation or association, as such are defined in RCW 84.34.250, with the original owner.
RCW 84.34.220