Wash. Rev. Code § 35.92.230
For the purpose of paying for a water right purchased by the city or town from the United States government where the purchase price has not been fully paid; paying annual maintenance or annual rental charge to the United States government or any corporation or individual furnishing the water for irrigation and domestic purposes, or either; paying assessments made by any water users' association; paying the cost of constructing or acquiring any system or means of distribution or delivery of water for such purposes; and for the upkeep, repair, reconstruction, operation, and maintenance thereof; accumulating reasonable operating fund reserves to pay for system upkeep, repair, operation, and maintenance, in such amount as is determined by the city or town legislative authority; accumulating reasonable capital fund reserves in an amount not to exceed the total estimated cost of system construction, reconstruction, or refurbishment, over such period of time as is determined by the city or town legislative authority; and for any expense incidental to such purposes, the city or town may levy and collect special assessments against the property within any district created pursuant to RCW 35.92.220, to pay the whole or any part of any such costs and expenses.
RCW 35.92.230