Wash. Rev. Code § 35A.08.110
If a majority of the votes cast at the election upon the adoption of the proposed charter favor it, certificates of election shall be issued to each officer elected at that election. Within ten days after the issuance of the certificates of election, the newly elected officers shall qualify as provided in the charter, and on the tenth day thereafter at twelve o'clock noon of that day or on the next business day if the tenth day is a Saturday, Sunday or holiday, the officers so elected and qualified shall enter upon the duties of the offices to which they were elected and at such time the charter shall be authenticated, recorded, attested and go into effect, and the city shall thereafter be classified as a charter code city. When so authenticated, recorded and attested, the charter shall become the organic law of the city and supersede any existing charter and amendments thereto and all special laws inconsistent therewith.
RCW 35A.08.110