Wash. Rev. Code § 43.180.190
Bonds issued under this chapter are hereby made securities in which all public officers and public bodies of the state and its political subdivisions, all insurance companies, trust companies in their commercial departments, savings banks, cooperative banks, banking associations, investment companies, executors, trustees and other fiduciaries, and all other persons whatsoever who are now or may hereafter be authorized to invest in obligations of the state may properly and legally invest funds, including capital in their control or belonging to them. Such bonds are hereby made securities which may properly and legally be deposited with and received by any state or municipal officer or any agency or political subdivisions of the state for any purpose for which the deposit of bonds and other obligations of the state are now or may hereafter be authorized by law.
RCW 43.180.190