RCW 81.20.060

Expenses of a complete valuation, rate and service investigation shall not be assessed against a public service company under this chapter if such company shall have been subjected to and paid the expenses of a complete valuation, rate and service investigation during the preceding five years, unless the properties or operations of the company have materially changed or there has been a substantial change in its value for rate making purposes or in other circumstances and conditions affecting rates and services.