WASH. REV. CODE ANN. §39.34.020. Definitions
Unless the context clearly requires otherwise, the definitions in this section apply throughout this chapter.
(1) “Public agency” means any agency, political subdivision, or unit of local government of this state including, but not limited to, municipal corporations, quasi municipal corporations, special purpose districts, and local service districts; any agency of the state government; any agency of the United States; any Indian tribe recognized as such by the federal government; and any political subdivision of another state.
(2) “State” means a state of the United States.
(3) “Watershed management partnership” means an interlocal cooperation agreement formed under the authority of RCW 39.34.200.
(4) “WRIA” has the definition in RCW 90.82.020.
WASH. REV. CODE ANN. §39.34.030 Joint powers — Agreements for joint or cooperative action, requisites, effect on responsibilities of component agencies — Financing of joint projects.
(1) Any power or powers, privileges or authority exercised or capable of exercise by a public agency of this state may be exercised and enjoyed jointly with any other public agency of this state having the power or powers, privilege or authority, and jointly with any public agency of any other state or of the United States to the extent that laws of such other state or of the United States permit such joint exercise or enjoyment. Any agency of the state government when acting jointly with any public agency may exercise and enjoy all of the powers, privileges and authority conferred by this chapter upon a public agency.
(2) Any two or more public agencies may enter into agreements with one another for joint or cooperative action pursuant to the provisions of this chapter: PROVIDED, That any such joint or cooperative action by public agencies which are educational service districts and/or school districts shall comply with the provisions of RCW 28A.320.080. Appropriate action by ordinance, resolution or otherwise pursuant to law of the governing bodies of the participating public agencies shall be necessary before any such agreement may enter into force.
(5) No agreement made pursuant to this chapter relieves any public agency of any obligation or responsibility imposed upon it by law except that:
(b) With respect to one or more public agencies purchasing or otherwise contracting through a bid, proposal, or contract awarded by another public agency or by a group of public agencies, any statutory obligation to provide notice for bids or proposals that applies to the public agencies involved is satisfied if the public agency or group of public agencies that awarded the bid, proposal, or contract complied with its own statutory requirements and either (i) posted the bid or solicitation notice on a web site established and maintained by a public agency, purchasing cooperative, or similar service provider, for purposes of posting public notice of bid or proposal solicitations, or (ii) provided an access link on the states web portal to the notice.
Link to the full statute can be found here: http://apps.leg.wa.gov/rcw/default.aspx?cite=39.34.030