Wash. Rev. Code § 35.34.250
Every city or town may create and maintain a contingency fund to provide moneys with which to meet any municipal expense, the necessity or extent of which could not have been foreseen or reasonably evaluated at the time of adopting the annual budget, or from which to provide moneys for those emergencies described in RCW 35.34.140 and 35.34.150. Such fund may be supported by a budget appropriation from any tax or other revenue source not restricted in use by law, or also may be supported by a transfer from other unexpended or decreased funds made available by ordinance as set forth in RCW 35.34.200. However, the total amount accumulated in such fund at any time shall not exceed the equivalent of thirty-seven and one-half cents per thousand dollars of assessed valuation of property within the city or town at such time. Any moneys in the emergency fund at the end of the fiscal biennium shall not lapse except upon reappropriation by the council to another fund in the adoption of a subsequent budget.
RCW 35.34.250