Wash. Rev. Code § 87.03.630
The board of directors of the district shall meet at the time and place specified in the notice and shall have full authority to determine all matters pertaining to the petition, including the denial as well as the granting of said petition or any part thereof; and if it appears at said hearing, or at any adjournment thereof which may be had not to exceed in all one hundred eighty days, that the land or any portion thereof petitioned to be included within the district, is susceptible of irrigation from the water supply and system of works of the said district and will be benefited by such irrigation; and if at said hearing or at any adjournment thereof as aforesaid, not more than fifty percent of the holders of title or evidence of title to the lands described in the petition and proposed to be included file their objections in writing to the inclusion of such land within the time and as provided in RCW 87.03.615 through 87.03.640, the said board shall make and enter in the records of their proceedings an order including said land, or such portion thereof as in their judgment is susceptible of irrigation and will be benefited as aforesaid, within the operation of said district.
RCW 87.03.630