Wash. Rev. Code § 8.12.040
When the corporate authorities of any such city shall desire to condemn land or other property, or damage the same, for any purpose authorized by this chapter, such city shall provide therefor by ordinance, and unless such ordinance shall provide that such improvement shall be paid for wholly or in part by special assessment upon property benefited, compensation therefor shall be made from any general funds of such city applicable thereto. If such ordinance shall provide that such improvement shall be paid for wholly or in part by special assessment upon property benefited, the proceedings for the making of such special assessment shall be as hereinafter prescribed, in this chapter: PROVIDED, That no special assessment shall be levied under authority of this chapter except when made for the purpose of streets, avenues, alleys, or highways or alterations thereof or changes of the grade therein or other improvements in or adjoining the same, or for bridges, approaches, culverts, sewers, drains, ditches, public squares, public playgrounds, public parks, drives or boulevards or for the purpose of draining swamps, marshes, tide flats, tidelands or ponds or for filling the same: AND IT IS FURTHER PROVIDED, That when a street, avenue, highway or boulevard is established or widened to a width greater than one hundred and fifty feet the excess over and above the one hundred and fifty feet shall be paid out of the general fund of such city without any deduction for benefits of such excess.
RCW 8.12.040