Wash. Rev. Code § 80.28.270
The commission's jurisdiction over the rates, charges, practices, acts or services of any water company or wastewater company includes any aspect of line extension, service installation, or service connection. If the charges for such services are not set forth by specific amount in the company's tariff filed with the commission pursuant to RCW 80.28.050, the commission shall determine the fair, just, reasonable, and sufficient charge for such extension, installation, or connection. In any such proceeding in which there is no specified tariffed rate, the burden is on the company to prove that its proposed charges are fair, just, reasonable, and sufficient.
RCW 80.28.270
Findings-Purpose-Limitation of chapter-Effective date- 2011 c 214 : See notes following RCW 80.04.010.