Cal. Pub. Util. Code § 102054

The district may operate and exercise the powers under this part within all or a part of the herein described unincorporated area of any county. However, the district shall have no power to levy an ad valorem property tax within any such unincorporated area, as provided in Article 7 (commencing with Section 102330) of Chapter 5 of this part, unless the board of supervisors of the county adopts a resolution declaring there is a need for the district to operate and levy a tax within the unincorporated area of the county or so much of the unincorporated area as described in the resolution.