Wash. Rev. Code § 8.12.250
If any city or town shall desire to take possession of any property or do any damage or proceed with any improvement, the compensation for which is to be paid for in whole or in part by the proceeds of special assessment under this chapter, it may advance from its general funds, or any moneys available for the purpose, the amount of the assessments aforesaid, and pay the same to the owner or into court, as herein provided, reimbursing itself for moneys so advanced from the special assessments aforesaid. If there be no funds available for the purpose, such city may contract indebtedness for the purpose of raising funds therefor, which indebtedness shall be contracted and such proceedings taken therefor as is provided by law for indebtedness contracted for other internal improvements.
RCW 8.12.250
Contracting indebtedness by city: Titles 35, 39 RCW.