Wash. Rev. Code § 85.38.140
The process by which budgets are adopted, special assessments are measured and imposed, rates and charges are fixed, and assessment zones are established, as provided in RCW 85.38.140 through 85.38.170, shall constitute an alternative optional method of financing special districts. A special district in existence prior to July 28, 1985, may conform with RCW 85.38.140 through 85.38.170 when its governing body adopts a resolution indicating its intention to conform with such laws. Whenever such a resolution is adopted, or a new special district is created on or after July 28, 1985, RCW 85.38.140 through 85.38.170 shall be the exclusive method by which the special district measures and imposes special assessments and adopts its budget. The governing body of a special district that was created before July 28, 1985, and which operates under RCW 85.38.140 through 85.38.170, may adopt a resolution removing the special district from operating under RCW 85.38.140 through 85.38.170, and operate under alternative procedures available to the special district. A county may charge a special district for costs the county incurs in establishing a system or systems of assessment for the special district pursuant to RCW 85.38.140 through 85.38.170.
RCW 85.38.140