ORS § 222.550
When the greater portion of a water district including a domestic water supply corporation or a water control district is thus withdrawn, measured by the comparative assessed valuations of the portion withdrawn and the portion remaining in the district, the remainder of the district may dissolve in the manner provided for water districts. If dissolution is determined upon and the city agrees to furnish water or other facilities theretofore provided by the water district to the remainder of the district and if the city agrees to assume the liabilities of the district, then all assets of the district become the property of the city. A city to which the major portion of a water district has been annexed may make such agreement notwithstanding any charter or statute limitation.
ORS 222.550