Wash. Rev. Code § 57.16.080
If any portion of the system after its installation is not adequate for the purpose for which it was intended, or if for any reason changes, alterations, or betterments are necessary in any portion of the system after its installation, then an improvement district with boundaries which may include one or more existing improvement districts may be created in the district in the same manner as is provided herein for the creation of improvement districts. Upon the organization of such an improvement district, the plan of the improvement and the payment of the cost of the improvement shall be carried out in the same manner as is provided herein for the carrying out of and the paying for the improvement in the improvement districts previously provided for in this title.
RCW 57.16.080
Part headings not law-Effective date-1996 c 230: See notes following RCW 57.02.001.