Wash. Rev. Code § 27.12.240
After a library shall have been established or library service contracted for, the legislative body of the governmental unit for which the library was established or the service engaged, shall appropriate money annually for the support of the library. All funds for the library, whether derived from taxation or otherwise, shall be in the custody of the treasurer of the governmental unit, and shall be designated by him or her in some manner for identification, and shall not be used for any but library purposes. The board of trustees shall have the exclusive control of expenditures for library purposes subject to any examination of accounts required by the state and money shall be paid for library purposes only upon vouchers of the board of trustees, without further audit. The board shall not make expenditures or incur indebtedness in any year in excess of the amount of money appropriated and/or available for library purposes.
RCW 27.12.240