Va. Code Ann. § 37.2-609

The exercise of the powers granted by this chapter shall be in all respects for the benefit of persons in the authority's service area and for the promotion of their safety, health, welfare, convenience, and prosperity. As the operation and maintenance of any behavioral health project that the authority is authorized to undertake will constitute the performance of an essential governmental function, the authority shall not be required to pay any taxes or assessments upon any behavioral health project acquired or constructed by it or on the revenues generated by its operation.