Va. Code § 21-228
Any integral body of territory within which are situated rivers, creeks or other watercourses or streams, not affected by ebb and flow of the tide, and none of which are embraced within any other sanitation district may, under the conditions and upon the taking and completion of the proceedings provided in this article, be created a sanitation district. Every part of the boundary of such a sanitation district shall either (1) coincide with the boundary of a county, city or town or (2) bisect a county, city or town, or (3) be located within one mile of the boundary of a county, city or town, or (4) consist of a straight line connecting two points each of which lies upon a boundary of one of the three types hereinabove described.
Va. Code § 21-228