Va. Code Ann. § 21-389

If at any time before or after the preparation of the assessment rolls or drainage tax lists the owners of any lands within the boundary of the drainage project, which are liable for assessments or are assessed, should sell the whole or part of the lands, the board of viewers together with the assistance of the drainage engineer of the project, or any other competent drainage engineer, shall so prepare or change the assessment rolls to provide for the change in liability due to the change of ownership of the lands or part thereof. The new owner's name shall be added to the assessment roll and shall thereafter be liable for the drainage assessment upon that portion of the land purchased.