Wash. Rev. Code § 35.67.194
Any and all water, sewer, or water and sewer revenue bonds part or all of which may have been heretofore (prior to June 8, 1955) issued by any city or town for the purpose of providing funds to pay part or all of the cost of acquiring, constructing, or installing a system of storm or surface water sewers or any part thereof necessary for the proper and efficient operation of a system of sanitary sewage disposal sewers or a sanitary sewage treatment plant, the proceedings for the issuance of which were valid in all other respects, are approved, ratified and validated, and are declared to be legal and binding obligations of such city or town, both principal of and interest on which are payable only out of the revenues of the utility or utilities pledged for such payment.
RCW 35.67.194