ORS § 553.710
After the creation of a subdistrict, and with the approval of the electors of the subdistrict, a water control district may enter into intergovernmental agreements under ORS chapter 190 for the construction of works within the subdistrict or outside of the subdistrict for the benefit of lands within the subdistrict. If by reason of an intergovernmental agreement a district becomes obligated to contribute all or any part of the cost of constructing such works or to furnish rights of way or to pay for the cost of improvements to be made in conjunction with the construction of such works or to maintain and operate the works after the construction thereof, the district may levy an ad valorem tax against the lands within the subdistrict for the purpose of raising funds with which to discharge its obligations under the agreement and to pay the costs and expenses incurred by the district in connection therewith. The levy of an ad valorem tax for such purposes shall be in lieu of and not in addition to any other method of levying assessments by a water control district.
ORS 553.710