The Trust Water Rights Program.  The state may acquire a trust water right by donation, purchase, or lease.  Trust water rights are placed in the state's Trust Water Rights Program and managed by the Department of Ecology (Ecology).  Two trust water rights systems, one for the Yakima River basin and the other for the rest of the state, are established in state law.

The Trust Water Rights Program enables the voluntary transfer of water and water rights to the state, either temporarily or permanently.  While a water right is held in trust, it is considered an exercised water right and is protected from relinquishment.  Water held in trust retains its original priority date.

Water Banks.  The process to establish a water bank begins with a consultation between Ecology's Water Resources Program and a would-be banker.  If Ecology agrees the banker's proposal is within the public's interest, a water banking agreement may be negotiated.  The agreement describes how Ecology will take ownership of a water right and hold it in the Trust Water Rights Program in exchange for processing applications for mitigated new uses.

Ecology is authorized to use water banking to mitigate for new water uses, hold water for beneficial uses consistent with terms established by the transferor, meet future water supply needs, and provide a source of water to third parties, on a temporary or permanent basis, for any allowed beneficial use.

Walla Walla Water Management Program.  Legislation passed in 2009 created the Walla Walla local water management program (Walla Walla program).  The local water management board was created, with representatives from city and county government, federally recognized Indian tribes, conservation districts, and water rights holders.  The board is authorized, among other duties, to assume the role of the local watershed planning unit, to administer the local water plan process, to manage banked water, to acquire water rights, and enter into agreements with water rights holders to not divert water that becomes available as a result of local water plans and water banking activities.

The Walla Walla program legislation authorized the board to establish a water bank in which surface and groundwater right holders may deposit their water rights on a permanent or temporary basis.  The board may manage those water rights to mitigate for impairment to instream flows and other existing water rights.

The Walla Walla program was initially scheduled to expire in 2019.  In 2019, legislation passed that moved the expiration date for the program to June 30, 2021.

Upon a request made by a water right holder to Ecology on or before June 30, 2021, a water right banked as part of the Walla Walla program must be accepted by Ecology as a temporary trust water right donation for up to two years, in the same quantity that the water right was banked as part of the Walla Walla program.