Va. Code § 21-181
Such fees, rents and charges being in the nature of use or service charges, shall as nearly as the commission shall deem practicable and equitable, be uniform throughout the district for the same type, class and amount of use or service of the sewage disposal system, and may be based or computed either on the consumption of water on or in connection with the real estate, making due allowance for commercial use of water, or on the number and kind of water outlets on or in connection with the real estate or on the number and kind of plumbing or sewage fixtures or facilities on or in connection with the real estate, or on the number or average number of persons residing or working on or otherwise connected or identified with the real estate or on any other factors determining the type, class and amount of use or service of the sewage disposal system, or on any combination of such factors.
Va. Code § 21-181